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Mapping the Pathways of Galaxy Transformation
Across Time and Space
Avalon, Catalina Island, California
July 31 - August 5, 2016
Session 1
Transitioning Galaxies in Clusters and Beyond (Bianca Poggianti ) . . . . . .
High Central Mass Density: Best Ticket to Cross the Blue to Red Bridge
(David Koo) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The death of galaxies: evolution through the post-starburst phase (Decker
French) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Resolving the Star Formation Quenching (Shoubaneh Hemmati ) . . . . . . .
To Quench or Not To Quench? How What We Say Affects What We Think
about Galaxy Evolution (Louis Abramson) . . . . . . . . . . . . . . . .
A Bayesian’s perspective of galaxy growth via bulge evolution (Josh Argyle)
Quasars Probing Galaxies: Gas Accretion in Extended Galactic Disks? (Crystal Martin) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Las Campanas PrISM Survey (Jeffrey Rich) . . . . . . . . . . . . . . .
Session 2
Observing the Consequences of Quenching in Simulations (Greg Snyder ) . .
Galaxy Zoo: Evidence for diverse morphologically dependent quenching histories across the green valley and the role of AGN feedback (Rebecca
Smethurst) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
BaLROG - Bars in Low-Redshift Optical Galaxies (Marja Seidel ) . . . . . .
The Role of Secular Evolution in Galaxy Transformation (Alison Crocker ) .
There and back again: pathways to and from the red-sequence for ISM rich
ETGs (Timothy Davis) . . . . . . . . . . . . . . . . . . . . . . . . . . .
Session 3
Galaxy Mergers on FIRE (Jorge Moreno) . . . . . . . . . . . . . . . . . . .
Probing Ionization Mechanisms and AGN Activity in Luminous Infrared Galaxies with Near-Infrared Spectroscopy (H.Jacob Borish) . . . . . . . . . .
Does AGN and stellar feedback affect the molecular gas in merger remnants?
(Junko Ueda) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Large Scale Outflows and Dense Outflows in low-z ULIRGs (George Privon)
The Role of Major Mergers in (obscured) Black Hole Growth and Galaxy
Evolution (Ezequiel Treister ) . . . . . . . . . . . . . . . . . . . . . . . .
Clumpy Star-formation in Local Luminous Infrared Galaxies (Kirsten Larson) 12
High-resolution cosmological simulations of major mergers: some merger remnants are star-forming and have stellar discs (Martin Sparre) . . . . . . 12
Rethinking the Narrative of a Micro-Merger: Impacts on the Host Galaxy
Morphology (Rachael Beaton) . . . . . . . . . . . . . . . . . . . . . . . 13
Session 4
TBD (Phil Hopkins) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Extreme Red Quasars in SDSS3-BOSS (Fred Hamann) . . . . . . . . . . . .
A Near-Infrared View of Shocks in Nuclear Outflows (Vivian U ) . . . . . . .
Star Formation Suppression due to AGN Feedback (Lauranne Lanz ) . . . . .
Star Formation in Luminous Quasars at 2<z<3 (Duncan Farrah) . . . . . .
Detailed visual morphologies of 200,000 galaxies at 0.25 < z < 4 from Galaxy
Zoo and Hubble Legacy Imaging (Brooke Simmons) . . . . . . . . . . .
Session 5
From Nuclear Outflows to Galactic Winds (Anne Medling) . . . . . . . . . .
Insights on the AGN-Galaxy Connection from CANDELS & X-UDS (Dale
Kocevski ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Cosmic Evolution of AGN Feedback: Insights from Broad-band Radio
Spectral Indices (Kristina Nyland ) . . . . . . . . . . . . . . . . . . . .
The Close AGN Reference Survey (Tanya Urrutia) . . . . . . . . . . . . . .
Galaxy evolution in dense environments (Simona Mei ) . . . . . . . . . . . .
Transforming Galaxies in Extreme Environments: the Era of Star Formation
and AGN Activity in Massive Clusters at z=1-2 (Stacey Alberts) . . . .
The Keck OSIRIS Nearby AGN Survey: Spatially Resolved Inflows and Outflows in Seyfert Galaxies (Francisco Muller-Sanchez ) . . . . . . . . . .
Mapping the incidence and distribution of AGN accretion across the galaxy
population (James Aird ) . . . . . . . . . . . . . . . . . . . . . . . . . .
Session 6
Environment and the Evolution of Dwarf Galaxies (Gurtina Besla) . . . . .
The Preferred Pathway to the Red Sequence (Jeremy Tinker ) . . . . . . . .
Dissecting z∼1 Galaxy Clusters in Phase-Space: Studying Star Formation
from the Outskirts to the Core (Allison Noble) . . . . . . . . . . . . . .
Effects of Local Envirnonment and Stellar Mass on Galaxy Quenching Out To
z ∼ 3 (Behnam Darvish) . . . . . . . . . . . . . . . . . . . . . . . . . .
The evolutionary pathways of dwarf galaxies (Federico Lelli ) . . . . . . . . .
It’s Complicated: Galaxy Evolution in Compact Groups (Sarah Gallagher ) .
Star formation suppression in galaxies in Hickson Compact Groups (Ute Lisenfeld ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Galaxy Evolution in Dense Group Environments: Clues from Warm Diffuse
Gas (Philip Appleton) . . . . . . . . . . . . . . . . . . . . . . . . . . .
Connecting dusty starburst galaxies and proto galaxy clusters: a case study
at z=2 (Chao-Ling Hung) . . . . . . . . . . . . . . . . . . . . . . . . .
Session 7
The Morphologies of the Most Luminous galaxies in the Universe (Jeyhan
Kartaltepe) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Giant cosmic tsunamis: the impact of galaxy cluster merger shocks on galaxy
evolution (Andra Stroe) . . . . . . . . . . . . . . . . . . . . . . . . . .
The Role of Environment in Transforming Galaxies Across Cosmic Time
(Gillian Wilson) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Latte Project: Simulating Satellite Dwarf Galaxies around a Milky Waymass Galaxy (Andrew Wetzel ) . . . . . . . . . . . . . . . . . . . . . . .
An emerging consensus on the merger rate of massive galaxies at z=0-3 (Allison W. S. Man) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Evolution of HI in Galaxies as a Function of Environment (Jessica Rosenberg) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The SAMI Galaxy Survey: The impact of the cluster environment on the star
formation of infalling galaxies (Matt Owers) . . . . . . . . . . . . . . .
Session 8
Galaxy transformations at z∼2 (Mariska Kriek ) . . . . . . . . . . . . . . . .
The mechanisms for quiescent galaxy formation at z<1 (Kate Rowlands) . .
How to quench massive galaxies (Andreas Faisst) . . . . . . . . . . . . . . .
The structures and star formation activities of massive galaxies in cosmological
simulations (Robert Feldmann) . . . . . . . . . . . . . . . . . . . . . . .
Evidence for a Significant Population of Massive Quenched Disks in the Early
Universe (Elizabeth McGrath) . . . . . . . . . . . . . . . . . . . . . . .
The gas content of galaxies over cosmic time (Gergely Popping) . . . . . . .
Structural transformation and quenching in massive post-starburst galaxies
(Omar Almaini ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Modelling dusty galaxies (Anna Sajina) . . . . . . . . . . . . . . . . . . . .
How fast can the Universe make a massive quiescent galaxy? (Pablo G. PerezGonzalez ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Session 9
Revealing the X-ray main sequence of star formation (Alison Coil ) . . . . .
JVLA and ALMA Spatially-Resolved Observations of Intensely Star-Forming
Regions in Galaxies at z ∼ 1-3 in the Hubble Ultra-Deep Field (Wiphu
Rujopakarn) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tracing the Inside-out Growth & Outside-In Quenching of Disks over ∼85%
of cosmic time. (David Wilman) . . . . . . . . . . . . . . . . . . . . . .
Poster Abstracts
The Shocked POststarburst Galaxy Survey (Katey Alatalo) . . . . . . . . . .
UV Colors of Shocked Poststarburst Galaxies (Felipe Ardila) . . . . . . . . .
Galactic Conformity from z=0.2-1 with PRIMUS (Angela Berti ) . . . . . . .
The Effect of the Cluster Environment on Galaxy Transformations (Pierluigi
Cerulo) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Clusters/Protoclusters of Starbursting Galaxies (David L Clements) . . . . .
FORMATION IN IR-BRIGHT AGNs (Y.Sophia Dai ) . . . . . . . . . .
Gas Loss By Ram Pressure Stripping and Internal Feedback from Low Mass
Milky Way Dwarf Satellites (Andrew Emerick ) . . . . . . . . . . . . . .
The geometry of the AGN obscurer in a hyperluminous quasar (Duncan Farrah)
TCB Flash: Constraining the Timescale for Satellite Quenching in Local
Group-like Environments (Sean Fillingham) . . . . . . . . . . . . . . .
Induced star formation in interacting galaxy pairs (Isaura L. Fuentes-Carrera)
Tracing the role of active nuclei in galaxy transformation: HI absorption surveys out to z = 1 (Marcin Glowacki ) . . . . . . . . . . . . . . . . . . .
MegaMorph and how it can identify key galaxy types (Boris Haeussler ) . . .
TBD (ChangHoon Hahn) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The GMRT 150MHz All Sky Survey (Preshanth Jagannathan) . . . . . . . .
Spectroscopic Bulge-Disc Decomposition of SDSS-IV/MaNGA Galaxies (Evelyn Johnston) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Quenching of star formation in massive galaxy clusters -Lynx W caught-inthe-act (Inger Jorgensen) . . . . . . . . . . . . . . . . . . . . . . . . .
Hidden in plain sight: Mass segregation using galaxy analogues in simulations
(Gandhali Joshi ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Distribution of Active Galactic Nuclei in Massive Galaxy Clusters at z∼1
(Wenli Mo) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Physical properties of star-forming and quiescent galaxies at z∼3 (Hooshang
Nayyeri ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Probing the transformation of galaxies in clusters at high-redshift using dynamical analyses (Lyndsay Old ) . . . . . . . . . . . . . . . . . . . . . .
Exploring the merger-starburst connection and its impact on the observed
bimodality in galaxy properties (Milena Pawlik ) . . . . . . . . . . . . .
Understanding the galaxy transformations leading to dwarf ellipticals (Reynier
Peletier ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TBD (Reynier Peletier ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
MHD simulations of ram pressure stripping of a disk galaxy (Mariana RamosMartinez ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Nearby velocity-offset AGN: signposts of double supermassive black holes?
(Hsin-Yi(Jenny) Shih) . . . . . . . . . . . . . . . . . . . . . . . . . . .
The MOSDEF Survey: Dissecting the star-formation rate vs. stellar mass
relation at z ∼ 2 (Irene Shivaei ) . . . . . . . . . . . . . . . . . . . . . .
Star Formation in Interacting vs. Spiral Galaxies in the Local Universe (Beverly Smith) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sizes and mass profiles of post-starburst galaxies at z∼1.5 (Katherine (Wren)
Suess) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The Importance of Black Hole Mass in the Physics Behind Quenching (Bryan
Terrazas) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Resolving distant quasar host galaxies with high angular resolution techniques
(Andrey Vayner ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Compact Groups in the Millennium Simulation (Trey Wenger ) . . . . . . . .
The prevalence of dwarf galaxy compact groups over cosmic time (Christopher
Wiens) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Author Index
Session 1
Transitioning Galaxies in Clusters and Beyond
9:00 - 9:30 am
Bianca Poggianti
I will discuss methods to identify galaxies in transition from being star-forming to
being passive, based on both integrated and spatially resolved spectroscopy of galaxies
in clusters and other environments at low redshift. I will present results obtained with
a large program with MUSE at the VLT, showing the relation between gas removal and
star formation activity, and discuss the conclusions that can be obtained from the star
formation rate-mass relation and the spectroscopic identification of recently quenched
High Central Mass Density: Best Ticket to Cross the Blue to
Red Bridge
David Koo
Univ. of Calif., Santa Cruz
I will report on several studies of field galaxies by our team that continue to favor
high stellar mass within the central 1 kpc radius as being the best ticket to cross the
bridge from being an active star forming galaxy to a quiescent one. Our studies range
from using SDSS for local galaxies to using the rich, deep, multi-wavelength imaging
and our Keck spectroscopic data in the CANDELS fields for redshift z ∼ 2 “nuggets”.
After normalizing for the evolution in both the star formation rate versus mass and
the central mass density thresholds needed for transformations at different masses, we
find a ””universal path”” or bridge that almost all field galaxies seem to take from
redshifts z ∼ 2 to today, whether by taking slow fading strolls or fast quenching dashes
to quiescence.
10:00 - 10:20 am
10:20 - 10:40 am
The death of galaxies: evolution through the post-starburst
Decker French
University of Arizona, Steward Observatory
Post-starburst (or ‘E+A’) galaxies are in transition between star-forming galaxies and
early-types, and represent a clear path for galaxies to transform from star-forming to
quiescence. Many show signs of a recent galaxy-galaxy merger and a newly-evolved
stellar bulge, and most have LINER-like emission, which may indicate low luminosity
AGN activity. Thus, the study of this short-lived phase of galaxy evolution can address
the connections among mergers, star formation history, and the evolution of the nucleus as a galaxy evolves onto the red sequence. Surprisingly, we have discovered that
many these galaxies, which are not currently forming stars, have significant reservoirs of
molecular gas, which may fuel the central, supermassive black hole or later star formation episodes. We have also found that post-starburst galaxies host a disproportionate
number of Tidal Disruption Events, in which a star is accreted onto the black hole. The
recent starburst in these galaxies allows us to put strong constraints on the details of
their recent star formation histories, and to place them on a timeline post-burst. I will
discuss these results and other new work detailing how their stellar populations, gas
content, and black hole properties evolve.
10:40 - 11:00 am
Resolving the Star Formation Quenching
Shoubaneh Hemmati
Internal secular evolution processes are known to be one of the main mechanisms responsible for the evolution of “global” properties of galaxies such as their star formation
activity, stellar mass assembly, and morphology. In this talk, I will illustrate the relation between global properties and kpc-scale substructures of galaxies out to z∼2.
Using combined high resolution data from the Hubble Space Telescope and long exposure spectroscopic observations with the Keck telescope, I produce 2D maps of physical
properties of galaxies such as rest-frame optical color, stellar mass and star formation
rate surface density, extinction and age as well as 1D profiles of nebular dust attenuation, and other diagnostic optical line ratios. I will present the resolved main sequence
of star formation inside individual galaxies with different global properties and discuss the potential use of this methodology in resolving the challenge of star formation
quenching by selecting galaxies at different environments.
To Quench or Not To Quench? How What We Say Affects
What We Think about Galaxy Evolution
11:30 - 12:00 pm
Louis Abramson
Is “quenching” the termination of star formation or the compression of star formation
histories (SFHs)? I discuss the deep implications this reframing has for what we see
as and how we study core processes shaping galaxy life-cycles. As a lens, I use two
outcomes from the IMACS Cluster-Building Survey: our finding that most z∼0.5 poststarbursts are rejuvenated passive galaxies, and a simple model positing that every
galaxy has a lognormal SFH whose parameters are set at birth. Both studies reinterpreted key metrics of galaxy evolution typically seen as ‘clear-cut’ evidence for one-way
quenching, causing our focus to shift from from mechanisms that stop SF to those
that accelerate evolution. They led to a paradigm in which the decline in activity
of SF galaxies since z∼2; the removal of systems from that population; and the correlations between environment, SFR, and morphology all reflect the same underlying
phenomenon: the initial configuration of the matter density field. This “density-driven
growth” and “starburst recycling” picture is quite different from the dominant “growand-quench” narrative, yet both describe the data well. As such, I contend that ours is
a viable alternative framework, but current observations are in fact too un-constraining
to confirm any description as “the best.” I close by reviewing new HST-derived results
that preview the kinds of discriminating data next-generation facilities will provide, enabling definitive tests of evolutionary models and the construction of a unique context
in which to set explanations.
A Bayesian’s perspective of galaxy growth via bulge evolution
Josh Argyle
University of St Andrews
Bulges play a pivotal role in how a galaxy might evolve. However, the exact mechanisms
involved in shaping their hosts and even their demographic evolution with cosmic time
still remain an unanswered piece in the galaxy formation puzzle. In this talk I will
present an innovative study into the stellar-morphological evolution of spheroidal and
spheroidal-disc galaxies over the redshift range 0< z < 3. We have combined a new
adaptive MCMC algorithm to decompose galaxy light into different structures and a
proper Bayesian model selection method to extract the most likely morphology. I will
present the results of our analysis based on a bulge-disc decomposition of ∼800 galaxies
with M* > 1010 M∗
12:00 - 12:20 pm
12:20 - 12:40 pm
Quasars Probing Galaxies: Gas Accretion in Extended
Galactic Disks?
Crystal Martin
UC Santa Barbara
”I will present new Keck LRIS spectroscopy of 50 galaxy – quasar pairs and describe
the kinematics of circumgalactic gas in typical, star-forming galaxies at redshift 0.2.
We find the Doppler shift of resonance absorption in MgII lies entirely to one side of
the galaxy systemic velocity. The sign of the net rotation
12:40 - 1:00 pm
The Las Campanas PrISM Survey
Jeffrey Rich
Carnegie Observatories
”The information gained from spatially resolved optical spectroscopy has proven crucial
to understanding the complete picture of galaxies and their contents. In order to fully
understand the interplay between the processes that govern and regulate star formation
and galaxy evolution we are building building a sample of the largest, highest spatial
resolution, and widest spectral coverage data cubes ever taken for nearby galaxies: the
Las Campanas PrISM Survey.
I will present recent results and ongoing work using our data cubes to map the ionized
ISM and its properties at spatial scales of order 10 pc in nearby galaxies such as M83
and NGC 300. The high spatial resolution of our data affords us the opportunity
to study the characteristics and total contribution of diffuse ionized gas, a less wellunderstood component of nearby galaxies, as well as metallicties, star formation rates
gas kinematics and more. I will also discuss how resolved spectroscopy can help detect,
quantify and distinguish between star formation, shocks, diffuse ionized gas and AGN
to help better inform larger, less resolved studies of galaxy properties.
Session 2
Observing the Consequences of Quenching in Simulations
Greg Snyder
2:30 - 3:00 pm
I will describe results on mergers, morphology, and quenching using mock data from
hydro simulations. From merger models, we created and analyzed thousands of synthetic spectra to reconcile the incidence of poststarburst galaxies with merger rates.
Currently, we are conducting mock surveys of the Illustris project to determine how
standard feedback models set correlations with galaxy structure, and to learn how mergers would appear in deep HST and JWST surveys. Without simulations and synthetic
data, we cannot reliably assign meaning to any given observed property. How should
we interpret rare and subtle features? Is a galaxy type rare because it is unimportant
or because it is short-lived? To answer such questions, we must measure observability
timescales, containing the information needed to convert number densities into physical
event rates. This requires creating realistic synthetic data from large simulation suites
and determining how these data connect to physical processes.
Galaxy Zoo: Evidence for diverse morphologically dependent
quenching histories across the green valley and the role of
AGN feedback
Rebecca Smethurst
University of Oxford
We present the results of a new Bayesian-MCMC analysis of the star formation histories
of over 126,000 galaxies across the colour magnitude diagram showing that diverse,
morphologically dependent quenching mechanisms are instrumental in the formation
of the present day red sequence. To do this we utilise the classifications from Galaxy
Zoo in a novel way, weighting by the vote fraction to include results from all galaxies
rather than using a threshold to split our sample into late- and early-type morphology.
We show that the rate at which quenching can occur is morphologically dependent in
each of the blue cloud, green valley & red sequence, and that the green valley is a
transition population for all morphological types, not a “red herring””. We discuss
3:00 - 3:20 pm
the nature of the possible quenching mechanisms which give rise to the distribution of
quenching parameters, considering the influence of the group and field environment,
secular evolution and mergers, both with and without black hole activity. We show
that a population of type 2 AGN host galaxies have recently (within 2 Gyr) undergone
a rapid (τ < 1 Gyr) drop in their star formation rate. We demonstrate that slower (τ >
2 Gyr) quenching rates dominate for high stellar mass (log10[M*/M ] > 10.75) hosts
of AGN with both early- and late-type morphology. The diversity of this new method
highlights that rapid quenching mechanisms cannot account fully for all the quenching
across the current AGN host population.We discuss how these results show that both
merger-driven and non-merger processes are contributing to the co-evolution of galaxies
and supermassive black holes across the entirety of the colour magnitude diagram.
3:20 - 3:40 pm
BaLROG - Bars in Low-Redshift Optical Galaxies
Marja Seidel
Carnegie Observatories
The plurality of existing galaxies in today’s Universe remains in many facets an enigma
in terms of their individual formation and evolutionary histories. While merging processes seem to have been especially dominant in the early Universe, the accelerating
expansion of it is drawing galaxies further apart and internal processes due to their own
morphology start having a crucial influence. One of the main drivers of this so-called
‘secular evolution’ are bars. Their significant departure from axisymmetry and the
associated torques are responsible for their ability to redistribute angular momentum
among the host galaxy as well as drive gas towards the center triggering star formation
and/or building up a central mass concentration. We use integral field observations
in combination with N-body simulations in order to better understand and quantify
their influence in nearby galaxies. While the effect of bars on global galaxy parameters
seems to be marginal, they seem to have a crucial influence in certain regions (resonance points), in particular altering the bulge. Our in-depth analyses using kinematics
and stellar populations support the longevity of bars, their similarity to the bulge and
difference to the disk as a structure rotating as a cylinder within the host galaxy.
The Role of Secular Evolution in Galaxy Transformation
Alison Crocker
4:50 - 5:20 pm
Reed College
This talk will summarize the roles of the secular evolution processes that are likely
involved in galaxy transformation or maintenance of that transformation. Secular processes here are defined to be those which do not involve the external influences of either
the environment or mergers and additionally to not require the input of an AGN. I will
outline the contributions of violent disk instabilities and bar-mediated gas concentration to spheroid (or pseudo-spheriod) creation, but focus more on the evidence for and
theory of morphological quenching. This process is invoked to explain the observed
lower star formation efficiencies of cold-gas hosting, bulge-dominated galaxies. If there
is time, I will discuss the maintenance role of hot gas halos around massive galaxies and
how precipitation from these hot gas halos periodically reinvigorate minor episodes of
star formation (as well as AGN activity).
There and back again: pathways to and from the red-sequence
for ISM rich ETGs
Timothy Davis
Cardiff University
In recent years it has become clear that a large fraction of ””quenched”” galaxies that
lie on the optical red sequence have a significant cold ISM, and are forming stars. This
begs the question: are these galaxies quenching, and near the end point of galaxy transformation? Or are they being regenerated? Using (sub-)millimetre data and optical
integral field spectroscopy (from MUSE, ATLAS3D, H-ATLAS & AlFoCS; the ALMA
Fornax Cluster Survey) along with semi-analytic and hydrodynamic simulations I will
show that the majority of this population are regenerated red-sequence galaxies, which
have begun to transform once more. In clusters, however, slower transformation mechanisms mean we may well be catching some galaxies as they transform for the first
time. That star-formation is regenerated in these objects has significant impact on the
interpretation of the trajectories of ETGs in the green-valley, and how these vary with
galaxy mass.
5:20 - 5:40 pm
Session 3
Galaxy Mergers on FIRE
Jorge Moreno
Cal Poly Pomona
Galaxy mergers and interactions are responsible for generating bursts of star formation,
for changing galactic morphology in dramatic ways, and for triggering single and dual
active galactic nuclei. In this talk, I will unveil the very first results from a novel suite of
high-resolution galaxy merger simulations, based on the ‘Feedback In Realistic Environments’ (FIRE) model. This model treats energy and momentum-driven feedback from
young stars and SN explosions explicitly, which acts directly on resolved star-forming
clouds within the ISM. Moreover, this framework relies on a new meshless Lagrangian
hydro code, GIZMO, which solves many problems associated with older solvers. Our
first work focuses on the spatial localization of star formation. In particular, we confirm
results from previous work: galaxy-galaxy interactions enhance nuclear star formation,
and suppress it at large galacto-centric radii (Moreno et al. 2015). However, two major
differences are found. First, star-formation enhancement and suppression are not as
dramatic as in older models. Secondly, the interaction-induced nuclear starburst has
a larger spatial extent. These differences are a reflection of the fact that, in our new
models, non-axisymmetric gravitational torques are not as effective at driving fuel into
the central regions as in older sub-grid based models. This suite of merger simulations is ideal for making predictions for, and interpreting results from, observations by
new-generation integral field spectroscopic surveys.
9:00 - 9:20 am
9:20 - 9:40 am
Probing Ionization Mechanisms and AGN Activity in
Luminous Infrared Galaxies with Near-Infrared Spectroscopy
H.Jacob Borish
University of Virginia
I present an analysis of ionization mechanisms in a sample of 47 luminous infrared
galaxies as traced by their near-infrared line emission. These galaxies are hotbeds of
extreme merger-driven star formation and are sometimes observed to contain luminous
AGN - both phenomenon are obscured by dust within the galaxies, necessitating the
need of long-wavelength data to assess the nature of their activity. The TripleSpec
spectra are characterized by strong line emission from hydrogen recombination lines, [Fe
II] lines, and ro-vibrational lines of molecular hydrogen. The [Fe II]/Pa-beta emission
line ratio are roughly correlated with the optical emission line classification, with the HII
region-like systems and LINERs having the lowest and highest values, respectively, of
the ratio. This result is broadly consistent with shocks being the dominant mechanism
driving this ratio. In addition, no evidence of embedded AGN (as traced via broad
line regions or emission from coronal lines) in narrow-line LIRGs with HII region-like
or LINER spectra were found. This study is part of the Great Observatories All-Sky
LIRG Survey (GOALS).
9:40 - 10:00 am
Does AGN and stellar feedback affect the molecular gas in
merger remnants?
Junko Ueda
Harvard-Smithsonian Center for Astrophysics
AGN and stellar feedback has been recently considered as an important process in
galaxy evolution because galactic winds and outflows driven by AGN and starburst
could blow out large amounts of the surrounding gas, quenching star formation. We
have conducted HCN (1-0) observations of 16 local merger remnants, which have molecular gas disks detected in the CO, using the Large Millimeter Telescope (LMT). These
merger remnants are taken from the sample of our ALMA/SMA study which reveals
that nuclear and extended molecular gas disks are common in the final stages of mergers. We find that half of 16 sources have large line widths of the HCN compared to
the CO. While the HCN line profiles of local galaxies have the same line widths as the
CO line, several galaxies with AGN and active nuclear starburst have large line widths
of the HCN. We thus suggest that the large line widths found in our sample may result from galactic winds and outflows driven by AGNs and starbursts. Furthermore,
we investigate the relation between the ratio of the line width (FWHM(HCN)/(CO))
and the size of the molecular gas disk. As a result, we find that sources with large
FWHM(HCN)/(CO) have compact molecular gas disks. If the large line widths of the
HCN result from AGN and stellar feedback, this suggests that the feedback may destroy
the molecular gas disks.
Large Scale Outflows and Dense Outflows in low-z ULIRGs
George Privon
10:00 - 10:20 am
Pontificia Universidad Catñlica de Chile
The coalescence stage of disk-disk galaxy mergers is thought to be a critical phase where
an buried AGN activates and joins with the starburst to clear gas from the nucleus and
quench star formation. The most spectacular example of this stage are the ULIRGs.
Outflows are nearly ubiquitous in these systems, but it not yet determined if these winds
escape the halo and whether the dense molecular gas goes along for the ride. Do the
winds disrupt the densest portions of the molecular ISM or do they merely remove the
lower-density molecular and atomic ISM, effectively ””starving”” the starburst. I will
show VLT/MUSE observations of the outflowing atomic wind in the dual AGN NGC
6240 and ALMA observations of a dense molecular outflow in the coalesced ULIRG
IRAS 13120-5453. These observations provide unique information on the character and
possible fate of the winds clearing the nuclear ISM.
The Role of Major Mergers in (obscured) Black Hole Growth
and Galaxy Evolution
Ezequiel Treister
P. Universidad Catolica, Chile
A clear picture is emerging in which rapid supermassive black hole (SMBH) growth
episodes (luminous AGN) are directly linked to major galaxy mergers, while the lower
luminosity AGN can be triggered by secular processes. In this scenario, the more
traditional unification paradigm in which orientation is the main parameter only holds
at lower luminosities, while for the more violent accretion events, triggered by major
mergers, we find evidence for an evolutionary sequence in which the AGN is first heavily
obscured (Compton-thick), to then reveal an unobscured quasar.
In this talk, I will present observational evidence in support of this scenario, both
in the local Universe and at high redshifts. In particular, I will discuss the main
results from a NuSTAR AO-1 program aimed to obtain high energy observations for
a sample of 12 nearby galaxies undergoing major mergers. These data allow us to
detect even heavily obscured SMBH growth episodes, including the detection for the
first time of a hidden AGN in NGC6286. Then, I will present the first results from our
program aimed to obtain optical and near-IR Integral Field Unit (IFU) spectroscopy
and ALMA maps for a sample of confirmed nearby dual AGN (separation <10 kpc),
including the archetypical galaxy NGC6240. Clear evidence for complex morphologies
and kinematics, outflows and feedback effects can be seen in these systems.
The importance of these high-luminosity, merger-triggered, obscured SMBH growth
episodes, identified in the IR as ULIRGs, for the cosmic history of SMBH growth and
its connection to galaxy evolution will be discussed.
11:30 - 12:00 pm
12:00 - 12:20 pm
Clumpy Star-formation in Local Luminous Infrared Galaxies
Kirsten Larson
Star-formation in high-z galaxies is often found to be concentrated in luminous starforming clumps much larger than those observed in the local universe. These large
clumps of star-formation are thought to be caused by high molecular gas fractions
and high turbulence. We present HST narrow-band imaging of Pa-beta and Pa-alpha
emission of 50 local Luminous Infrared Galaxies from the Great Observatory All-Sky
LIRG Survey (GOALS). LIRGs are often highly disturbed systems undergoing major
mergers with molecular gas fractions of ∼10 - 50%. We can therefore study how the
size, number and luminosity of the clumpy star-formation varies with MGF and merger
stage. These data allow us to study spatially resolved HII regions down to 60pc and
directly compare to star-forming clumps found in both local and high-z galaxies. We
find star-forming clumps in the local LIRGS of similar sizes to those resolved in local
normal galaxies (60 - 400pc radius) but with higher luminosities that fit between those
found in normal local galaxies and those at z∼2.
12:20 - 12:40 pm
High-resolution cosmological simulations of major mergers:
some merger remnants are star-forming and have stellar discs
Martin Sparre
HITS, Heidelberg Institute for Theoretical Studies
I present a suite of cosmological zoom-in simulations of major mergers run with the
moving-mesh code, AREPO. The simulated galaxies have a z=0 mass comparable to
the Milky Way, and they are simulated with a 40 times finer mass resolution than the
Illustris simulation. I will show how the galaxy morphology of major merger remnants
behave: In all the simulations a major merger at z=1 reduces the strength of the disc,
but in several cases the merger remnant regrow a new significant disc before z=0. Also,
a fraction of the major merger remnants are not quenched, but remains star-forming
with blue colours. I will show how the stellar metallicity distribution function in merger
remnants at z=0 has a memory of the merger that happened at z=1. This will have
direct implications for galactic archaeology studies. This is one of the first studies of
major mergers in cosmological simulations, since most of the existing literature about
mergers relies on idealised non-cosmological setups.
Rethinking the Narrative of a Micro-Merger: Impacts on the
Host Galaxy Morphology
Rachael Beaton
Carnegie Observatories
In the Lambda-CDM paradigm, Milky Way sized galaxies are assembled via many
minor- (1:5 to 1:10 mass ratio) and micro-mergers (less than 1:10 mass ratio) of dwarf
satellite companions over cosmic time. Artifacts of such events are preserved by the
large dynamical timescales within the stellar halo, where many stellar debris can be
found in abundance with the haloes of the Local Group. While these known debris are
quite diverse in morphology, they are almost uniformly consistent with being old or
ancient events. Understanding the earlier phases of these accretions and the potential
impact on the parent galaxy is left to extrapolation from their current fossilized state.
In a survey for micro-merger debris within the Local Volume (with D=50 Mpc), I have
discovered tidal debris with surviving satellites, whose morphologies defy the ‘norm’ of
the Local Group. Two exciting examples are the bright satellite of NGC 5387, which
is currently in undergoing a starburst (Beaton et al. 2014) and IC 2209 (interacting
with NGC 2460), whose interaction debris contain a ridge of HII regions (Beaton et al.
in prep.). The dynamical morphologies of the stellar tidal debris estimate that these
interactions are relatively young, with the debris forming in less than 1 Gyr – suggesting
that these mergers could offer unique insight on the early stages of micro-mergers not
probed locally. I use N-body modelling to study the later evolution of the accretion
event, in particular its impact on the parent galaxy, and global morphology metrics
to ‘blindly’ classify these interacting systems (Beaton et al., submitted). Comparing
snapshots from the models to deep imaging of other disturbed systems, I build a more
dynamic narrative for events at the micro-merger mass scale and demonstrate, despite
intuition, that events at the micro-merger mass scale have the potential to impact the
inferred properties of the host galaxy.
12:40 - 1:00 pm
Session 4
Phil Hopkins
2:30 - 3:00 pm
Extreme Red Quasars in SDSS3-BOSS
Fred Hamann
UC Riverside
Dust-reddened quasars are believed to mark an early stage of massive galaxy evolution
where declining star formation rates are accompanied by blowouts of gas and dust that
provide our first visible views of a luminous central AGN. The recent Baryon Oscillation Spectroscopy Survey (BOSS) of SDSS-III discovered many more faint quasars with
higher redshifts and redder colors than any previous large survey. I will describe studies that combine BOSS spectra with SDSS and Wide-Field Infrared Survey Explorer
(WISE) photometry of nearly 100,000 z > 2 quasars to identify red quasars and characterize trends in the quasar properties with reddening. We find a number of strong
trends consistent with a young evolution stage. For example, red quasars are 5 to 8
times more likely to have all varieties of ””intrinsic”” absorption lines in their spectra,
including broad absorption lines (BALs) and their narrower cousins (mini-BALs) that
identify strong quasar-driven outflows. Red quasars also tend to have emission line
spectra resembling narrow-line Seyfert 1s, which are believed to have high accretion
rates (L/Ledd). Perhaps most surprising is a new population of extreme red quasars
(ERQs), selected via rest-frame UV to near-IR colors similar to Dust Obscured Galaxies
(DOGs), that we find to have uniquely exotic emission line properties such as highly
blueshifted CIV emission lines and the broadest and most blueshifted [OIII] lines ever
recorded (with FWHMs and blue wings reaching 5000 km/s). These extreme [OIII]
lines strongly favor a unique evolution stage involving galaxy-scale blowouts. We now
have ongoing ALMA sub-mm observations of several ERQs to measure the star formation rates and search for signs of disturbance/‘feedback’ in the molecular gas (CO, [CI])
in their host galaxies.
3:20 - 3:40 pm
3:20 - 3:40 pm
A Near-Infrared View of Shocks in Nuclear Outflows
Vivian U
UC Riverside
The role of shocks in quenching star formation and subsequently driving galaxy evolution is growing increasingly prominent with the advent of emission line modeling and
integral field observations that help to identify and understand these processes. Shocks
are particularly important phenomena in galaxy mergers where violent interaction of
gas takes place in the interstellar medium of the systems. However, advanced optical
tools used in these diagnostics encounter challenges at both physical and technical levels, e.g. shocks and other photoionization processes are difficult to discern using only
optical lines, and that the nuclei of these merger systems are often dusty and optically thick. With high-resolution near-infrared integral-field observations taken with
OSIRIS on Keck, I will present how we rely on near-infrared diagnostics such as the
ro-vibrationally excited H2 and Br gamma lines to identify and characterize shocks
associated with nuclear outflows seen in our merger systems. The resulting tools and
calibrations will become progressively important for understanding galaxy evolution as
we enter the era of JWST and new infrared instruments on 30-meter class telescopes.
4:50 - 5:10 pm
Star Formation Suppression due to AGN Feedback
Lauranne Lanz
Feedback due to active galactic nuclei is one of the key components of the current
paradigm of galaxy evolution; however our understanding of the process remains incomplete. Radio galaxies with strong rotational H2 emission provide an interesting
window into the effect of radio jet feedback on their host galaxies, since the large
masses of warm (>100 K) H2 cannot solely be heated by star formation, instead requiring jet-driven ISM turbulence to power the molecular emission. I will discuss the
insights multiwavelength observations of 22 H2 luminous radio galaxies yield on the
impact of AGN jets on the star formation activity in these galaxies.
Star Formation in Luminous Quasars at 2<z<3
Duncan Farrah
5:10 - 5:30 pm
Virginia Tech
We investigate star formation rates in optically selected, luminous type 1 quasars at
2<z<3 using stacked Herschel observations. The star formation rates remain approximately constant with redshift, with a mean rate of 300 M /yr. This is consistent with
the processes that trigger quasars evolving in a similar way to the processes that trigger
star formation, and with the bulk of star formation in quasar hosts at this epoch not
being in the ‘starburst’ mode. We find higher rates of star formation in quasars with
higher accretion rates, and propose that we observe such a relation because the free
gas fraction is higher at z>2, making the correlation easier to discern, and because
that short-term AGN variability introduces scatter that is averaged out in our stacking
analyses. We also find higher star formation rates in quasars with higher black hole
masses, and argue that this result is at least to some extent independent of the relation with accretion luminosity. The two relations are plausibly driven by the available
free gas, and how efficiently this gas is channeled into the nuclear regions, respectively.
These relations together could also explain why we see no clear relation between star
formation rate and Eddington luminosity. We observe a decline in star formation rate
with increasing CIV equivalent width. This decline can be partially explained as a
manifestation of the Baldwin effect, but likely has an additional contribution from a
scaling with black hole mass. Conversely, we find no systematic relation between star
formation rate and the asymmetry of CIV, suggesting that AGN winds do not affect
star formation on timescales comparable to the AGN duty cycle.
Detailed visual morphologies of 200,000 galaxies at 0.25 < z <
4 from Galaxy Zoo and Hubble Legacy Imaging
Brooke Simmons
UC San Diego
From 2010 to 2015, over 150,000 people contributed over 12,000,000 independent visual
classifications of approximately 200,000 galaxies imaged using the ACS and WFC3
cameras as part of the AEGIS, CANDELS, COSMOS, GEMS, and GOODS surveys.
Here we present the combined, weighted, debiased visual morphological classifications
of these galaxies. Measurements include details of clump structures, bar features, spiral
arm counts, bulge strength in disks, and merger/tidal features. The classifications agree
very well with professional visual classifications. We show first results from the data
sets, including basic demographics of the samples, and identify subsamples of spiral,
clumpy, and merging galaxies at a range of redshifts. The data releases for the ACS and
WFC3 classifications are imminent (expected by late summer 2016, once the papers are
accepted); those desiring early access to the data need only ask.
5:30 - 5:50 pm
Session 5
From Nuclear Outflows to Galactic Winds
Anne Medling
2:30 - 3:00 pm
Australian National University
The evolution of a galaxy depends heavily on its gas content: gas both forms stars and
fuels black hole growth. These processes may be capable of self-regulating, since both
star formation and AGN activity can drive outflows that may remove gas from the host
galaxys reservoir. Such outflows are challenging to study because of the wide range
of scales involved. Distinguishing between launching mechanisms requires high spatial
resolution, but such observations usually are too limited in field-of-view to determine
what effect an outflow has on galactic scales. I will present some first results from our
two-pronged approach, which combines wide-field optical integral field spectroscopy
tracing galactic winds on several kpc scales and AO-assisted near-infrared integral field
spectroscopy to zoom in on the launch regions of these winds. The combination of these
observations is a powerful way to connect the physical mechanisms driving galactic
winds to the physical effects these winds can have on their host galaxies.
Insights on the AGN-Galaxy Connection from CANDELS &
Dale Kocevski
Colby College
I will summarize the insights gained from the CANDELS and X-UDS surveys regarding
the demographics of the AGN host population out to z∼2. In particular, I will focus on
1) the high frequency of disturbed morphologies among heavily obscured, compton-thick
AGN at z∼1-2 and 2) the prevalence of luminous AGN in compact, star forming galaxies
at z=2.5. The former result suggests that merger-triggered AGN at z∼1 are heavily
obscured, which may help explain why it has been so difficult to clearly establish an
AGN-merger connection. The latter result suggests SMBH growth, and possibly AGN
feedback, was ubiquitous in ‘blue-nugget’ galaxies at z∼2. Based on their size, stellar
mass, and star formation rates, these galaxies appear to be the direct progenitors of the
compact ‘red nugget’ population. Our findings indicate the first generation of quenched
3:00 - 3:20 pm
galaxies emerged in the early Universe directly following a phase of rapid SMBH growth.
I will discuss what these observations reveal about the connection between AGN activity
and the rise of the red sequence at z∼2.
3:30 - 3:40 pm
The Cosmic Evolution of AGN Feedback: Insights from
Broad-band Radio Spectral Indices
Kristina Nyland
Although our knowledge of the physics of galaxy formation and evolution has made great
strides over the past few decades, we still lack a complete understanding of how the
first galaxies formed at high redshift, the details of the complex symbiotic relationship
between galaxies and their supermassive black holes (SMBHs), and the mechanisms
responsible for triggering and halting the vigorous star formation (SF) and nuclear
activity in galaxies during the ‘peak epoch’ of galaxy assembly. While the next generation of radio telescopes are expected to usher in many exciting advancements in this
area of research, existing wide-area surveys from telescopes such as the GMRT, JVLA,
and ATCA can already provide interesting constraints. Here, I present a preliminary
analysis of the 150 to 1400 MHz radio spectral indices of objects identified in the five
multiwavelength deep fields that comprise the Spitzer Extragalactic Representative Volume Survey (SERVS). In addition to identifying high-redshift radio galaxies in SERVS,
I compare the broad-band radio spectral indices with various host galaxy properties,
such as photometric redshift, to investigate implications on the cosmic evolution of
AGN feedback.
3:40 - 4:10 pm
The Close AGN Reference Survey
Tanya Urrutia
Leibniz Institut fúr Astrophysik, Potsdam
In galaxy evolution simulations, the AGN phase is thought to be special in transforming a galaxy, especially through the so-called AGN feedback, which shuts down
star formation and/or leaves it turned off. Observational evidence for this is much
more scarce: while AGN outflows are ubiquitous, their predicted vast effects on the
host galaxy is tenuous and confined to a few spectacular examples. In my talk, I will
present CARS (, the Close AGN Reference Survey, which studies
35 local, luminous, Type 1 AGN. The backbone of the survey is data from the MUSE
3d spectrograph, which maps out in detail spatial and spectral information about the
host galaxy, but much multiwavelength ancillary data exists for these objects. I will
show statistically how outflow properties (strength, mass, ionization potential) correlates with certain AGN properties, especially the accretion rate. I will also show some
spectacular examples of the so-called “green wisps” (large AGN-ionized regions in the
host galaxy). As the name says, the observations done with CARS will act as a reference point for the higher redshift Universe and make predictions on the peak of AGN
activity at z∼2.
Galaxy evolution in dense environments
Simona Mei
4:50 - 5:10 pm
Observatory of Paris/University of Paris Denis Diderot
We believe that elliptical galaxies formed the bulk of their stellar population in dense
regions at redshift of z∼2.5-3, and then evolved passively up to the present. Galaxy
clusters and proto-clusters are the ideal environments to study the formation and evolution of early-type galaxies, and early probes of cosmology. Clusters at z>1.5 are shown
to host the star forming progenitors of their current red sequence early-type population. We will present our recent cluster and protocluster detections in the HST CDF-S,
CANDELS and SSDF fields using deep observations with Spitzer, the HST/WFC3
grism spectroscopy and VLT/KMOS IFU spectroscopy. We will discuss our results in
terms of galaxy evolution and the formation of the massive early-type progenitors.
Transforming Galaxies in Extreme Environments: the Era of
Star Formation and AGN Activity in Massive Clusters at
Stacey Alberts
Steward Observatory, University of Arizona”
It is well established that galaxy properties are connected to their environment, with
local massive galaxy clusters representing the extreme, populated primarily by passively
evolving early-type galaxies with very little star formation or black hole accretion activity. Cluster assembly models have long predicted that the last major epoch of mass
growth and star formation (SF) activity in massive clusters occurred in short bursts at
very high redshift (z∼3-5); however, recent studies have begun to reveal that clusters at
z=1-2 contain significant SF and AGN activity, on par with or even in excess of lower
density environments. This epoch, then, represents an important opportunity to study
the effect of environmental mechanisms on the transition of galaxies from blue to ’red
and dead’.
In this work, we present a detailed, multi-wavelength study of SF and AGN activity
in 11 near-infrared selected, massive (log M > 14 M ) galaxy clusters at 1<z<1.75.
Utilizing optical to far-infrared imaging from Herschel/PACS, we characterize the spectral energy distributions (SEDs) and dust-obscured SF properties of cluster galaxies in
relation to their environment. Identification and decomposition of AGN through SED
5:10 - 5:30 pm
fitting allows us to include the contribution to cluster SF from AGN hosts and quantify
the AGN fraction as a function of cluster-centric radius and redshift. In good agreement
with recent studies, we find that cluster galaxies at z>1.4 have field-like SF activity
right into the cluster cores, followed by a transition toward significant quenching by
z∼1. AGN also show a significant rise in activity in cluster cores, with clusters at z>11.5 showing an excess in their AGN fraction over that found in the field. This indicates
that environmental triggering of AGN is efficient in massive clusters during this epoch.
Lastly, we constrain the timescale of cluster galaxy quenching by comparing Ha from
our HST observations, which traces SF on short (∼10 Myr) timescales to our infrared
SF, which traces longer timescales (∼100 Myr). We find that the ratio of these tracers
is correlated with cluster-centric radius, indicating recent quenching in cluster galaxies.
Taken together with other clues from the literature, these results paint a clearer picture
of the role of environment in galaxy evolution.
5:30 - 5:50 pm
The Keck OSIRIS Nearby AGN Survey: Spatially Resolved
Inflows and Outflows in Seyfert Galaxies
Francisco Muller-Sanchez
University of Colorado at Boulder
”I present the first results from the KONA (Keck OSIRIS Nearby AGN) survey, which
uses the integral field unit OSIRIS plus LGS adaptive optics to probe down to scales of
5-30 parsecs in a sample of 40 Seyfert galaxies. In this talk, I will describe recent work
showing how AGN are fed and how they influence their host galaxies. We find that
AGN-driven outflows of ionized gas are ubiquitous, and that biconical models of radial
outflow provide a good fit to the spatially resolved kinematics. Inflows of molecular
gas are found in approximately half of the sources, where they occur mostly in nuclear
spiral structures or nuclear bars with mass inflow rates of ∼0.1-10 M yr-1. This is of
the order of the outflow rates, suggesting that AGN feedback suppresses accretion onto
the supermassive black hole (SMBH). Furthermore, the kinetic power of the outflow
follows a relationship with the velocity dispersion of the molecular gas in the central
25 pc, but this becomes indiscernible when the large-scale dispersion is considered.
This suggests that AGN feedback has a strong impact on the turbulent ISM near the
SMBH, but not on the galaxy disk. Finally, our observations provide direct evidence
of the ways in which the outflows of ionized gas interact with the circumnuclear ISM,
either by creating cavities of molecular gas, or by launching molecular outflows.
Mapping the incidence and distribution of AGN accretion
across the galaxy population
James Aird
University of Cambridge
To understand the role of AGN in the transformation of the galaxy population throughout cosmic time, we must determine how the incidence of AGN and the distribution of
their accretion power depends on the physical properties of the galaxies that host them.
We combine near-infrared selected samples of galaxies from the CANDELS/3D-HST
and UltraVISTA surveys with deep Chandra X-ray data to provide new constraints
on the distribution of specific accretion rates (scaled relative to the total host galaxy
mass) within both star-forming and quiescent galaxy populations as a function of stellar
mass and redshift. Our results reveal a broad underlying distribution of accretion rates
(reflecting long-term variability in the level of AGN fuelling) in both galaxy types. The
probability of a star-forming galaxy hosting an AGN (above a fixed specific accretion
rate) shows a strong stellar mass dependence revealing a higher incidence of AGN in
massive host galaxies and undergoes a stellar-mass-dependent evolution with redshift.
The probability of a quiescent galaxy hosting an AGN is generally lower but does not
depend on stellar mass and evolves differently with redshift. Our results show that
the levels of black hole growth are closely linked to the transforming galaxy population
and provide vital constraints on any potential impact of AGN on the transformation
5:50 - 6:10 pm
Session 6
Environment and the Evolution of Dwarf Galaxies
Gurtina Besla
9:00 - 9:30 am
University of Arizona
Low mass, dwarf galaxies (M∗ = 1e8 - 5e9 Msun) are typically gas rich, unless found
in proximity to a massive host. This has lead to the conclusion that the evolution of
dwarfs is dominated solely by their host environment, through processes such as tidal
and ram pressure stripping. Turning the argument around, this also implies that dwarfs
are ideal probes of the circumgalactic medium (CGM) and dark matter potentials of
their hosts. However, dwarf galaxies are often found with companions, invoking an
additional environmental pathway for their evolution. Recent results from the TiNy
Titans Survey illustrate that dwarf-dwarf galaxy interactionscan be an important mode
of gas removal, causing these galaxies to possess large envelopes and streams of gas.
Such extended structures can be efficiently stripped upon entering a more massive
environment, highlighting an overlooked mode of gas supply to the CGM of galaxies
like our Milky Way.
The Preferred Pathway to the Red Sequence
Jeremy Tinker
New York University
I combine group catalogs from SDSS data with high-resolution N-body simulations
to statistically determine the preferred pathway to the red sequence: group or field
processes. In the parlance of halo occupation, these equate to processes that impact
satellite and central galaxies. This method quantifies the timescale of the migration
to the red sequence. I will show that field processes are the dominant pathway to
the z=0 red sequence, and that the migration timescales are substantially different for
central and satellite galaxies of the same stellar mass. Additionally, I will present new
measurements of the scatter between halo mass and galaxies mass, yielding constraints
on the correlation between halo growth and stellar growth as well as the ‘duty-cycle’ of
star formation.
9:30 - 9:50 am
9:50 - 10:10 am
Dissecting z∼1 Galaxy Clusters in Phase-Space: Studying Star
Formation from the Outskirts to the Core
Allison Noble
University of Toronto
Understanding the influence of environment is a fundamental goal in studies of galaxy
formation and evolution. High-redshift galaxy clusters offer ideal laboratories with
which to examine environmental effects as infalling galaxies morph from star-forming
to red and dead galaxies within the cluster core. In Noble et al. 2013, we presented
a novel definition for environment using the phase space of line-of-sight velocity and
clustercentric radius, which probes the time-averaged density to which a galaxy has
been exposed and traces out accretion histories. Using this dynamical definition of
environment revealed a decline in specific star formation towards the cluster core in
the earliest accreted galaxies, and was further shown to isolate post-starburst galaxies
within clusters (Muzzin et al. 2014). We have now extended this work to higher-redshift
clusters at z=1.2 using deep Herschel-PACS and -SPIRE data (Noble et al. 2016). With
a sample of 120 spectroscopically-confirmed cluster members, we investigate various
galaxy properties as a function of phase-space environment for dynamically distinct
galaxy populations, namely recent infalls and those that were accreted onto the cluster
at an earlier epoch. These properties are then compared to a field sample of starforming galaxies at 1.1 < z < 1.2 to shed light on cluster-specific processes in galaxy
evolution. In this talk I will discuss the various implications of a phase-space definition
for environment, and present our most recent results, focusing on how this accretionbased definition aids our understanding of quenching mechanisms within z=1.2 galaxies.
I will conclude with brand new results from ALMA Cycle 3 observations of some of the
first molecular gas detections in the cores of three galaxy clusters at z=1.6.
10:10 - 10:30 am
Effects of Local Envirnonment and Stellar Mass on Galaxy
Quenching Out To z ∼ 3
Behnam Darvish
California Institute of Technology
We study the effects of local environment and stellar mass on galaxy properties using
a mass complete sample of quiescent and star-forming systems in the COSMOS field
at z . 3. We show that at z . 1, the median star-formation rate (SFR) and specific
SFR (sSFR) of all galaxies depend on environment, but they become independent of
environment at z & 1. However, we find that only for star-forming galaxies, the median
SFR and sSFR are similar in different environments, regardless of redshift and stellar
mass. We find that the quiescent fraction depends on environment at z . 1, and on
stellar mass out to z ∼ 3. We show that at z . 1, galaxies become quiescent faster in
denser environments and that the overall environmental quenching efficiency increases
with cosmic time. Environmental and mass quenching processes depend on each other.
At z . 1, denser environments more efficiently quench galaxies with higher masses
(log(M/M )&10.7), possibly due to a higher merger rate of massive galaxies in denser
environments, and that mass quenching is more efficient in denser regions. We show
that the overall mass quenching efficiency (mass ) for more massive galaxies (log(M/M
)&10.2) rises with cosmic time until z ∼ 1 and flattens out since then. However, for less
massive galaxies, the rise in mass continues to the present time. Our results suggest
that environmental quenching is only relevant at z . 1, likely a fast process, whereas
mass quenching is the dominant mechanism at z & 1, with a possible stellar feedback
The evolutionary pathways of dwarf galaxies
Federico Lelli
Case Western Reserve University
The mechanisms that transform gas-rich dwarf irregulars (dIs) into gas-poor dwarf
ellipticals (dEs) are still unclear. Starburst dwarf galaxies are transition-type, fastevolving systems, which may hold the key to understand such mechanisms. We study
the structure and dynamics of 18 starburst dwarfs at z=0, combining interferometric
HI observations with HST imaging of resolved stellar populations. We also consider
control samples of non-starbursting dIs in the group/field environment and dEs in the
Virgo cluster. We reach the following results. (1) Starburst dwarfs have gas fractions
similar to dIs, indicating that stellar feedback did not eject large amounts of gas out of
their potential wells. Gas consumption or expulsion are not viable mechanisms for the
transformation of gas-rich dwarfs into gas-poor dEs. (2) The inner rotation curves of
starburst dwarfs rise more steeply than those of typical dIs, pointing to an unusual concentration of mass (gas, stars, and dark matter). Some “compact” dIs and rotating dEs,
however, show similarly steep rotation curves and are potential descendants of starburst
dwarfs. (3) Starburst dwarfs have more asymmetric outer HI distributions than dIs,
suggesting that starbursts are triggered by interactions/mergers between dwarf galaxies
or cold gas accretion from the IGM.
10:30 - 11:00 am
11:30 - 12:00 pm
It’s Complicated: Galaxy Evolution in Compact Groups
Sarah Gallagher
Western University
Compact groups of galaxies host a handful of galaxies within a few galaxy radii of
each other. With low relative velocities and high number densities, galaxies in this
environment interact strongly and over extended time periods, and thus dynamical
galaxy evolution is enhanced. At the same time, the small membership means that
these groups remain imprinted with their early history: their initial relative positions
and velocities influence strongly their current properties. These low-mass systems are
thus ideally suited to test galaxy evolution in the dense, low-mass environments that
were likely building blocks of galaxy clusters and isolated ellipticals. I’ll synthesize
the results from a mult-wavelength observational and theoretical effort to map the
baryons and reconstruct the recent history of local compact groups with the aim of
understanding galaxy evolution in this important environment.
12:00 - 12:20 pm
Star formation suppression in galaxies in Hickson Compact
Ute Lisenfeld
Universidad Granada (Spain)
Galaxies in Hickson Compact Groups (HCGs) live in an environment where galaxy
interactions play an important role. Mid-infrared colours from the Spitzer and WISE
are able to classify galaxies in blue, star-forming and red quiescient objects. Galaxies
with intermediate colour, populating the so-called “canyon” region are rare.
I will present an analysis of the molecular gas and SF properties of a sample of galaxies
in HCG with CO data. We find that the star formation efficiency and also the molecularto-stellar mass is lower in canyon compared to blue galaxies, indicating that a loss of
molecular gas and suppression SF is crucial in the morphological transition.
Galaxy Evolution in Dense Group Environments: Clues from
Warm Diffuse Gas
Philip Appleton
12:20 - 12:40 pm
Caltech/NASA Herschel Science Center
”Due largely to spectrometers onboard Spitzer and Herschel, our understanding of the
energetics of warm diffuse gas in compact groups has provided new insight into largescale processes shaping gas in dense environments. I will review the progress that has
been made in understanding how energy is driven into the ISM of host galaxies through
both galaxy-galaxy collisions, and feedback from starburst or AGN-driven winds, using
both ground-based IFU and space-based observations. Ranging from turbulent heating
of the intra-group medium in Stephans Quintet, to outflows and winds in other systems,
I will discuss processes that can change the state of molecular gas in galaxies. How might
theses processes suppress star formations, and for how long? Can shocks and turbulence
transform galaxies or are they merely tracers of activity? I will discuss the importance
of understanding warm molecular and diffuse atomic gas in high redshift systems, and
how new opportunities emerge from the capabilities of JWST, WFIRST, ALMA and
SPICA. The possibility of detecting turbulent warm molecular gas at very high-z will
be reviewed in the context of a possible future NASA far-IR surveyor mission. ”
Connecting dusty starburst galaxies and proto galaxy clusters:
a case study at z=2
Chao-Ling Hung
University of Texas at Austin
The cores of massive galaxy clusters are dominated by elliptical galaxies with minimal
star formation, but the pathways that lead to these massive, quenched galaxies remain
unclear. Proto galaxy clusters at z>2 with rich populations of submillimeter galaxies
(SMGs) and dusty star-forming galaxies (DSFGs) represent important sites and critical
phases where/when the massive cluster galaxies are actively assembling. I present our
search of DSFGs within and around a protocluster at z∼2.1 in the COSMOS field.
Both color-selected SFGs and DSFGs show significant overdensities around the protocluster, and this structure spans across several tens of cMpc, considerably larger than
previously observed. The cluster core and the extended DSFG- and SFG-rich structure
together demonstrate an active cluster formation phase, in which the cluster is accreting a significant amount of material from large scale structure while the more mature
core may begin to virialize. Along with other DSFG-rich protoclsuters and protocluster
candidates, I discuss if these intense star formers are triggered concurrently through
galaxy interactions and/or enhanced gas supply, and how do these mechanisms may
lead to subsequent quenching.
12:40 - 1:00 pm
Session 7
The Morphologies of the Most Luminous galaxies in the
Jeyhan Kartaltepe
Rochester Institute of Technology
In the local universe, Ultraluminous Infrared Galaxies (ULIRGs, LIR > 1012 L ) are
all interacting and merging systems. To date, studies of ULIRGs at high redshift have
found a variety of results due to their varying selection effects and small sample sizes.
Some studies have found that mergers still dominate the galaxy morphology while
others have found a high fraction of morphologically normal or clumpy star forming
disks. Near-infrared imaging is crucial for interpreting galaxy structure at high redshift
since it probes the rest frame optical light of a galaxy and thus we can compare directly
to studies in the local universe. At high redshift (z∼2), not only are ULIRGs much more
common, but many more of the extreme HyLIRGs (LIR > 1013 L ) are detected. We
have recently obtained HST WFC3-IR imaging of a sample of high-z HyLIRGs over the
wide area COSMOS field in order to study their morphology and determine if they are
the analogs of ULIRGs in the local Universe. In this talk, I will present our first results
on the merger origin of these extreme systems, and compare them to CANDELS results
of LIRGs and ULIRGs at the same redshift, thereby probing a luminosity range of over
two orders of magnitude at the peak epoch in star formation activity and spanning a
range of parameter space in the SFR-M* plane.
2:30 - 3:00 pm
3:00 - 3:20 pm
Giant cosmic tsunamis: the impact of galaxy cluster merger
shocks on galaxy evolution
Andra Stroe
The galaxy population in relaxed clusters is dominated by passively evolving ellipticals.
However, a large fraction of clusters are undergoing mergers, which in the most extreme
cases, give rise to cluster-wide traveling shocks. Is the galaxy population in merging
clusters dominated by passive galaxies? How do merger shocks interact with cluster
galaxies? Through Halpha, HI and radio mapping of galaxy clusters at low redshift
(z∼0.2) we uncover, for the first time, whether shocks inhibit or trigger star formation
in cluster galaxies. We find that in young clusters undergoing a merger, the passage of
the shock through gas-rich cluster galaxies can compress the gas and lead to vigorous
star formation lasting for a few 100 Myr, reversing the typical environmental trends
operating in galaxy clusters. The complex interaction between the merger, the shock
wave and gas can ultimately accelerate the quenching of gas-rich star-forming galaxies.
Shock induced star formation may a fundamental driver in the evolution of protoclusters and high-redshift clusters, where mergers and shocks were far more common
than in the nearby Universe.
3:20 - 3:40 pm
The Role of Environment in Transforming Galaxies Across
Cosmic Time
Gillian Wilson
University of California Riverside
Despite a dramatic build up in the number of quenched galaxies at z < 2, it is still
unclear how this quenching comes about. Potential quenching mechanisms fall into
two categories: processes that act on ””centrals”” and those that act on ””satellites””.
While both hydrodynamic and semi-analytic models do a good job of predicting the
quenched fraction of centrals, they over predict the fraction of quenched satellite galaxies, reflecting our much greater uncertainty about how ””environmental”” quenching
I will present results from GCLASS, a 25-night Gemini/GMOS spectroscopic follow-up
survey of ten massive clusters at z∼1, and explain what we are learning about quenching and stellar mass assembly of galaxies in these, the densest of environments, relative
to the field population. In particular, I will discuss evidence for a change in the dominant satellite galaxy quenching mechanism at z=1 relative to the local universe. I will
conclude by discussing GOGREEN and DEEPDRILL, two new large surveys approved
by Gemini & Spitzer, designed to study the effects of environment at lower stellar mass
and at higher redshift, respectively. Collectively, these powerful new surveys are beginning to allow us to place constraints on the location and timescale of quenching and,
in concert with both hydro-simulations and semi-analytic models, identify the complex
role of environment in shaping galaxy transformation over cosmic time.
The Latte Project: Simulating Satellite Dwarf Galaxies
around a Milky Way-mass Galaxy
3:40 - 4:10 pm
Andrew Wetzel
Carnegie Observatories & Caltech
The Latte Project is a new suite of cosmological zoom-in baryonic simulations that
model the formation of Milky Way-mass galaxies at parsec-scale resolution, using the
FIRE (Feedback in Realistic Environments) model for star formation and stellar feedback. These simulations self-consistently resolve the satellite dwarf galaxy populations
that form around the Milky Way-mass host galaxies, including the relevant physics to
model their stellar populations. I will discuss the relative impacts of (internal) stellar
feedback and (external) environment on the star formation histories, stellar kinematics,
and chemical enrichment histories of these simulated dwarf galaxies, including comparisons with the observed dwarf galaxies around the Milky Way and Andromeda.
An emerging consensus on the merger rate of massive galaxies
at z=0-3
Allison W. S. Man
European Southern Observatory
At the peak of cosmic star formation history at z∼2, galaxy mergers are typically
identified via close pair selections. Searches for satellites are limited to the most massive
galaxies due to the NIR survey sensitivity limits. While the LCDM predicts that their
merger rate increases monotonically with redshift, almost all observations indicate that
the merger rate is nearly constant out to z∼3. We argue that a considerable fraction of
mergers are missed in current searches based on optical and NIR data. At z>1, satellites
can contain comparable gas and stellar masses. This implies that a population of gasrich (likely dusty) satellites can be missed in stellar-mass limited searches. I will present
how ALMA is used to identify these missing gas-rich satellites around massive galaxies.
While this will mitigate the tension between the observed vs LCDM-predicted merger
rate of massive galaxies, it may imply that our current constraints on the merger-driven
mass and size growth of massive galaxies may be incomplete.
4:50 - 5:10 pm
5:10 - 5:30 pm
The Evolution of HI in Galaxies as a Function of Environment
Jessica Rosenberg
George Mason
Galaxies in the local universe possess a wide range of properties due, at least in part,
to their merger history and environment. I will discuss our use of optical and HI 21
cm data (from SDSS and ALFALFA) to study the gas and stars in galaxies as a way of
tracing the impact of pair interactions as well as the group and cluster environment on
the gas content of galaxies. We find that interacting pairs show little change in their
HI gas content as the interaction progresses while there is evidence for gas depletion
towards the center of galaxy groups, and even more significant depletion towards the
center of galaxy clusters, likely driven by ram pressure stripping. These results indicate
that the group and cluster environments play an crucial role in the evolution of gas in
galaxies in the local universe.
5:30 - 5:50 pm
The SAMI Galaxy Survey: The impact of the cluster
environment on the star formation of infalling galaxies
Matt Owers
Macquarie University and Australian Astronomical Observatory
The star-forming properties of galaxies that reside in the dense cores of galaxy clusters
are remarkably different from those in the field; quiescent early-type galaxies are much
more prevalent in cluster cores whereas star-forming spirals dominate in the field. These
differences must be reconciled with the hierarchical nature of large-scale structure formation, where the cluster galaxy population increases by the accretion of galaxies from
lower density environments. The dominant mechanism responsible for transforming
infalling galaxies, cluster-related or otherwise, remains elusive. Getting to the heart
of this issue requires a robust definition of galaxy environment, along with resolved
information on the recent star formation history of the infalling galaxies.
The SAMI Galaxy Survey will provide resolved spectroscopy for around 3600 galaxies.
Of those galaxies, 700 have been selected to be members of eight massive clusters of
galaxies. A redshift survey conducted on the AAT’s AAOmega multi-object spectrograph provided a sample of 3000 confirmed cluster members that have been used to
characterize the dynamical properties of each cluster. In particular, the redshift survey
has allowed a robust characterization of the projected phase-space (PPS) distribution
of the clusters. The position of a galaxy in PPS can be used as a proxy for the time
since infall for a galaxy. In this talk, I will present an analysis of the resolved starforming properties of SAMI cluster galaxies which, based on their position in PPS,
are very likely to be encountering the cluster core for the first time. The majority of
these galaxies show ongoing star-formation their centers, but show evidence for young
(<1Gyr) stellar populations with no ongoing star-formation in the outer parts of the
disk. This indicates that the galaxies are having their star formation quenched from
the outside-in, likely due to the effects of ram-pressure stripping as they traverse the
Session 8
Galaxy transformations at z∼2
Mariska Kriek
9:00 - 9:30 am
UC Berkeley
In the past years it has become clear that the massive galaxy population at z∼2 was
much more diverse than today, ranging from compact quiescent to large star-forming
galaxies. The relation between these two populations and their possible evolutionary
connection are still poorly understood. If these galaxy types indeed are evolutionary
connected, how do the star-forming galaxies quench and shrink into the quiescent galaxies? Or is there a different population of progenitors for the compact quiescent galaxies?
New studies based on CANDELS, ALMA, and deep near-infrared spectroscopy with
MOSFIRE give new insights into these questions. In this talk I will present several
projects that make use of the populations of post-starburst and compact star-forming
galaxies for understanding the formation of z∼2 compact quiescent galaxies are their
connection to star-forming galaxies at similar redshift.
The mechanisms for quiescent galaxy formation at z<1
Kate Rowlands
University of St Andrews
One of the key problems in modern astrophysics is understanding how and why galaxies switch off their star formation, building the ‘red-sequence’ that we observe in the
local Universe. Post-starburst (‘E+A’) galaxies, where a galaxy has recently undergone a massive starburst, are sufficiently common at z∼1-2 that they may contribute
significantly to the growth of the red-sequence at this important epoch (Wild et al.
2009, 2016). It is not well known how much post-starburst galaxies contribute to the
build-up of the red sequence at z<1, due to small number statistics in previous redshift surveys, and aperture bias at very low redshifts (e.g. in SDSS). By exploiting
the highly complete, wide-area GAMA and VIPERS spectroscopic surveys, we select
post-starburst galaxies undergoing rapid quenching (<1 Gyr timescales), green-valley
galaxies undergoing slower quenching and red sequence galaxies. We chart the build-up
of the red sequence over the last 8 billion years and find that <10% of galaxies on the
9:30 - 9:50 am
red sequence could have gone through a post-starburst phase. The majority of galaxies
at low redshift undergo a much slower decline in their star formation before reaching
the red sequence. This picture is consistent with the recent detection of significant
amounts of residual cold gas in local PSB galaxies (Rowlands et al. 2015, French et
al. 2015), indicating that multiple events may be required to transform a low redshift
star-forming galaxy into a future quiescent galaxy.
9:50 - 10:10 am
How to quench massive galaxies
Andreas Faisst
The time-scale over which quenching of star-formation is happening is closely related to
the actual quenching mechanism and therefore offers a tool to understand the physics of
the shut-down of star-formation. However, very little is known about these time-scales.
We use a sample of 400 very massive (logM > 11.4) galaxies at z ∼ 2 in the COSMOS
field to investigate their quenching time-scale and possible mechanism using their trajectories in the 3-dimensional phase space spanned by stellar mass, SFR, and galaxy
size. In more detail, we predict the size evolution of quenched galaxies from star-forming
galaxies assuming two possible mechanisms: the ‘waning model’ (cut off of gas flow on
galaxy leading to its consumption over >500 Myrs) and the ‘instantaneous-quenching
model’ (instantaneous gas depletion by a merger-induced star-burst). We find that an
’instantaneous-quenching’ model best reproduces the observed size evolution of quiescent galaxies at logM>11 and therefore conclude that such massive galaxies have to
quench on short time-scales of several 100 Myrs. The high merger rates of such galaxies
strengthen this picture of merger-induced star-formation quenching.
10:10 - 10:30 am
The structures and star formation activities of massive
galaxies in cosmological simulations
Robert Feldmann
University of California, Berkeley
The properties of galaxies changed dramatically between z∼2-3 and today. The specific
star formation rates of typical star forming galaxies decreased by an order of magnitude
and the number of quiescent galaxies grew strongly. In addition, a significant fraction
of massive galaxies at early times were highly compact with effective radii of 1 kpc or
below, while similarly massive galaxies with such small radii are extremely rare today.
I will discuss the transformational processes that affect the star formation and size
evolution of massive galaxies with the help of the MassiveFIRE project, a set of stateof-the-art cosmological simulations of massive galaxies and their environments over
cosmic time. In particular, I will show that the halo accretion rate is a key parameter
in determining which massive galaxies at z∼1.5-3 become quiescent. Furthermore, I
will discuss the compact sizes of massive, quiescent galaxies at early times and the
size growth between z∼3 and z=0. If time permits, I will evaluate (based on mock
data derived from the simulations) how well future observations with JWST will help
constrain global properties of massive galaxies at intermediate redshifts.
Evidence for a Significant Population of Massive Quenched
Disks in the Early Universe
Elizabeth McGrath
10:30 - 11:00 am
Colby College
Using CANDELS, we select a sample of massive (>1010 M ), quiescent galaxies at z>1
to explore the relationship between morphology and star-formation quenching in the
early universe. While observations in the local Universe suggest that the mechanism
responsible for quenching star formation is linked to the structural transformation from
disk to spheroid, we find a significant fraction (∼30%) of disk-dominated galaxies among
the quiescent population at high redshift, far in excess of what we find today. The
persistence of stellar disks long after star-formation has ceased implies that in at least
some cases quenching precedes morphological transformation. We examine formation
scenarios for these massive quiescent disks as compared with their quiescent spheroid
counterparts, and discuss possible quenching mechanisms.
The gas content of galaxies over cosmic time
Gergely Popping
ESO Garching
The star-formation activity of our Universe increased from early epochs (z∼6), peaked
around z=2, and then decreased by an order of magnitude until present age. To fully
appreciate the physical origin of the star-formation activity of our Universe we need
to focus on the gas content of galaxies over cosmic time. The most recent versions
of cosmological models of galaxy formation explicitly include the detailed tracking of
the atomic and molecular hydrogen content of galaxies and make predictions for the
sub-mm lines emission from species such as CO, HCN, and [CII]. New semi-empirical
approaches provide data-driven predictions for the atomic and molecular gas content
of galaxies. I will discuss the predictions made by these different types of models for
the HI and H2 content of galaxies and their sub-mm line emission, and the inferred
gas properties of 25000 galaxies at redshfits 0.5 < z< 3, taken from the CANDELS
survey. I will present results such as a weak evolution in the HI content and HI mass
function of galaxies, strong evolution in the H2 content of galaxies, weak evolution in
the cosmic density of HI, the evolution of atomic and molecular gas in dark matter
11:30 - 12:00 pm
haloes, and predictions for CO luminosity functions. I will finish by demonstrating how
a comparison between theoretical models of galaxy formation and observed and inferred
gas masses can reveal caveats in our understanding of galaxy physics.
12:00 - 12:20 pm
Structural transformation and quenching in massive
post-starburst galaxies
Omar Almaini
University of Nottingham
Despite many years of study, we still do not fully understand why massive galaxies
abruptly switch off their star formation in the distant Universe. It is also unclear if
the same processes are responsible for the morphological transformation of galaxies,
to produce the Hubble Sequence we observe today. The rare class of post-starburst
(‘E+A’) galaxies provide a unique opportunity to study the transition phase, but until
recently only a handful had been identified at high redshift (z>1). Using a new PCA
technique, we have recently identified over 500 post-starburst galaxies in the UKIDSS
UDS field, spanning the redshift range 0.5<z<2.0 (Wild et al. 2016; Maltby et al.
2016). We find that their space density is sufficient to provide a major growth channel
for massive quiescent galaxies. We also find that post-starburst galaxies at high redshift
(z>1) are surprisingly compact and spheroidal, with a distribution of Sersic indices
that are indistinguishable from the old quiescent population. We conclude that the
quenching of star formation occurs during (or after) the event that forms the protospheroid. Our findings are consistent with a scenario in which compact massive galaxies
are formed from extremely gas-rich dissipative collapse, with rapid quenching followed
by a gradual growth in size.
12:20 - 12:40 pm
Modelling dusty galaxies
Anna Sajina
Tufts University
I will present current work on comparing GADGET+Sunrise hydrodynamic simulations with observations of IR-luminous galaxies at z∼0.3-3. I will especially focus on
the relative roles of stars and AGN in heating the dust, how this changes throughout a
merger stage and as a function of AV . I will compare the results of the simulations with
empirical measurements. I will address the successes and limitations of the current generation of hydrodynamic simulations. Lastly, I discuss a new MCMC-based luminosity
function evolution code in development at Tufts and how it combines with the above
efforts to constrain the role of AGN and star-formation activity in the IR luminosity
function through cosmic time.
How fast can the Universe make a massive quiescent galaxy?
Pablo G. Perez-Gonzalez
Universidad Complutense de Madrid
We will discuss our results about the Star Formation Histories (SFHs) of massive
(M> 1010 M ) quiescent galaxies (MQGs) at z>1. These SFHs have been inferred
from the analysis of rest-frame ultraviolet/optical spectro-photometric data from the
SHARDS and Hubble Space Telescope Wide Field Camera 3 (HST/WFC3) G102 and
G141 surveys of the GOODS-N field. Taking advantage of the SHARDS data resolution, we are able to break the typical degeneracies inherent to most stellar population
studies by measuring UV and optical absorption indices. The population of MQGs
at z>1 shows a duality in their properties. Dead galaxy samples at these redshifts
are dominated (at the 80-85% level) by systems with relatively young mass-weighted
ages, tM <2 Gyr, and short star formation timescales, 60-200 Myr. The evolution of
these so-called mature galaxies from z<1 to z= 0 is consistent with being passive, but
accompanied with a stellar mass increase not affecting the mean ages. There is also
an older population of ‘senior galaxies’ (15% of the sample) with tM =2-4 Gyr, longer
star formation timescales, around 400 Myr, and larger masses, log(M/M )∼10.8 (0.3
dex larger than the mature population). The number density of this sub-population
of senior galaxies is consistent with that found for massive quiescent galaxies at z∼2,
implying that those galaxies did not restart their star formation activity once they were
quenched. We find that the derived SFHs for our MQGs are consistent with the slope
and the location of the Main Sequence (MS) of star-forming galaxies at z>1.0, when
our galaxies were 0.5-1.0 Gyr old. According to the derived SFHs, all of the MQGs
experienced a Luminous Infrared Galaxy (LIRG) phase during typically 500 Myr and
roughly half of them went through an Ultra Luminous Infrared Galaxy (ULIRG) phase
for 100 Myr. Based on average mass-weighted ages for massive galaxies at z < 1 we
find that that the build-up of the red sequence is continuous down to z∼1, and only
below that redshift (in the last 6 Gyr), the evolution of massive galaxies is dominated
by quiescence.
12:40 - 1:00 pm
Session 9
Revealing the X-ray main sequence of star formation
Alison Coil
2:30 - 3:00 pm
UC San Diego
We present measurements that reveal an ‘X-ray main sequence’ of star formation over
a wide range of redshifts and stellar masses, providing new, independent constraints
on the slope and evolution of the star forming main sequence. Our results are based
on large, stellar-mass limited samples of star-forming galaxies selected at near-infrared
wavelengths in the CANDELS/3D-HST and UltraVISTA surveys. We use deep Chandra imaging to extract X-ray information for all galaxies in our sample and use an
advanced Bayesian technique to recover the intrinsic distribution of luminosities, pushing substantially below the nominal X-ray detection limits. Our distributions exhibit a
clear peak at low X-ray luminosities that is associated with star formation. By tracking
the luminosity of this peak as a function of stellar mass and redshift we reveal the X-ray
main sequence, with a slope of ∼0.6, a normalization that evolves strongly with redshift, and no evidence for a turn-over or flattening at high stellar masses. Comparing
to tracers of star formation at other wavelengths indicates that X-rays are providing a
robust, relatively direct, yet independent tracer of the average star formation rates of
JVLA and ALMA Spatially-Resolved Observations of
Intensely Star-Forming Regions in Galaxies at z ∼ 1-3 in the
Hubble Ultra-Deep Field
Wiphu Rujopakarn
Kavli IPMU, University of Tokyo
We utilize extremely sensitive blank-field surveys at radio and millimeter bands from
the Jansky Very Large Array (JVLA) and Atacama Large Millimeter Array (ALMA)
in the 2’ x 2’ Hubble Ultra-Deep Field to study the distribution of star formation in
five galaxies and six X-ray AGN hosts at z = 1-3. The JVLA and ALMA images at
6 cm and 1.3 mm reach sensitivities of 0.33 and 31 uJy/beam rms at 0.3” and 0.4”
resolutions, respectively. Together, they reveal a direct and spatially-resolved view of
3:00 - 3:20 pm
intensely star-forming regions within each galaxy that is independent of dust extinction
and uncontaminated by old stellar populations. We will present the morphology of
star formation in relation to old stellar populations, size and SFR surface density, gas
fraction, and discuss the implications on outflows and evolution of these intensely starforming (yet typical, i.e., SFR*) systems at the peak epoch of galaxy evolution.
3:20 - 3:40 pm
Tracing the Inside-out Growth & Outside-In Quenching of
Disks over ∼85% of cosmic time.
David Wilman
With radial profiles of HAlpha emission from a unique combination of KMOS3D and
HAGGIS surveys, I will describe how star formation drives the spatial growth, evolution
and quenching of galaxy disks over ∼85% of cosmic time. The 75 night KMOS3D survey
on the VLT with up to 20hour on-source in 600+ mass-selected galaxies at z∼0.7-2.8
traces star formation and the kinematics of the ionized gas into the outer disk. Most
galaxies at this gas-rich epoch contain turbulent star forming disks which are more
extended than their stellar disks, even in galaxies with low SFR for their stellar mass.
In the local Universe, in contrast, HAlpha profiles from HAGGIS demonstrate that the
star forming disks of most central galaxies are similar in size to their stellar disks, while
outside-in removal of star forming gas is common, especially in satellite galaxies of
group-mass halos. These also have compact stellar disks and anti-truncated stellar disk
profiles, emphasizing the role of gravitational processes. Our combined results suggest
that the evolution of disk galaxies is characterized by galaxy-wide, rapid accretion and
star formation at z>1 and by the slower, more subtle accumulation of gravitational and
stripping effects on an otherwise stable, low mass star forming disk at lower redshifts.
Poster Abstracts
The Shocked POststarburst Galaxy Survey
Katey Alatalo
Carnegie Observatories
Modern day galaxies are found to be in a bimodal distribution, both in terms of their
morphologies, and in terms of their colors, and these properties are inter-related. In
color space, there is a genuine dearth of intermediate colored galaxies, which has been
taken to mean that the transition a galaxy undergoes to transform must be rapid.
Given that this transformation is largely one-way (at z=0), identifying all initial conditions that catalyze it becomes essential. The Shocked POststarburst Galaxy Survey
( is able to pinpoint transitioning galaxies at an earlier stage of
transition than other traditional searches.
UV Colors of Shocked Poststarburst Galaxies
Felipe Ardila
There exist multiple pathways through which galaxies can transition from blue, gas-rich,
star-forming disks to red, gas-poor, quiescent spheroidals. Most post-starburst searches
only detect galaxies after they have quenched their star formation and already transformed, thus missing objects with additional mechanisms for ionizing the remaining gas.
The Shocked POststarburst Galaxy Survey (SPOGS) aims to identify galaxies in this
transitional phase with nebular lines which are excited from shocks rather than star formation processes. We explored the UV properties of these objects with NUV and FUV
photometry from archival data of the Galaxy Evolution Explorer(GALEX) for 759 of
the 1067 objects in SPOGS. The remaining objects were either not within the GALEX
footprint, or not significantly detected within the data in both bands. Any available
GALEX images containing the object (across multiple surveys of varying depth)were
coadded to obtain the deepest possible intensity map of each object. Photometry was
performed using the Source-Extractor Kron (AUTO) aperture setting, and validated
with the GALEX catalog of discrete sources (GCAT) available in the NASA/IPAC
Extragalactic Database (NED). The goal of this project was to obtain UV photometry
for as many SPOGS objects as possible, in order to compare these objects to other
post-starburst galaxies in color-mass, color-magnitude, and star-formation rates. This
will provide significant insight on this transforming phase of a galaxy’s life, and allow
us to better understand these SPOGS objects.
Galactic Conformity from z=0.2-1 with PRIMUS
Angela Berti
UC San Diego
We test for galactic conformity from z=0.2-1.0 to a projected distance of 5 Mpc using
spectroscopic redshifts from the PRism MUlti-object Survey (PRIMUS). Our sample
consists of ∼60,000 galaxies in five separate fields covering a total of ∼5.5 square degrees, which allows us to account for cosmic variance. Dividing our sample into starforming and quiescent galaxies using a cut in specific star formation rate, we identify
star-forming and quiescent “isolated primary” galaxies. We match the redshift and stellar mass distributions of these samples, to control for correlations between quiescent
fraction and redshift and stellar mass. We detect a significant conformity signal (>3
sigma) of ∼5% on scales of 0-1 Mpc and a 2.5-sigma signal of ∼1% on scales of 1-3
Mpc. We also test for redshift and stellar mass dependence of the conformity signal
within our sample.
The Effect of the Cluster Environment on Galaxy
Pierluigi Cerulo
Universidad de Concepcion
Clusters of galaxies are the most massive virialised cosmic structures. They host a
diversity of environments, from the dense cores to the sparse outskirts, providing observational laboratories for testing the theories of galaxy interactions. Clusters are
characterised by a prominent red sequence and an over-abundance of early-type galaxies with respect to the field, indicating that their galaxy members undergo significant
transformations from blue, star-forming and spiral-like to red, quiescent and bulgedominated. I present the results from the study of a sample of 9 clusters at 0.8 < z
< 1.5 from the HAWK-I Cluster Survey (HCS, Lidman et al. 2013). We find that
the build-up of the red sequence is accelerated in clusters with respect to the field,
suggesting that the mass of the host dark matter halo is a crucial parameter in setting
the timescales for star formation quenching. Further, we find that the red sequence in
z∼1 clusters is dominated by elliptical galaxies at all luminosities, while in local clusters it becomes dominated by S0 galaxies at magnitudes fainter than M*. This result
suggests that faint S0 galaxies are a late addition to the red sequence, resulting from
the transformation of red, passive spiral galaxies. I discuss the implications of these
results in the general framework of galaxy and cluster evolution and give an overview
of my current and ongoing work on the HCS sample.
Clusters/Protoclusters of Starbursting Galaxies
David L Clements
Imperial College London
The combination of Herschel and Planck data allows us to search for groups of far-IR
luminous sources over large fractions of the extragalactic sky. This work has uncovered
a significant population of what appear to be galaxy clusters/proto-clusters where several member galaxies are undergoing near-simultaneous major bursts of star formation.
These far-IR luminous galaxies may be gas and dust rich spiral-type galaxies transforming into the dust and gas poor elliptical galaxies that dominate galaxy clusters
today. Observations of these sources are ongoing to confirm their nature, determine
their evolutionary status, and to examine the physical processes that might be behind
the high star formation rates seen. It is already clear that these objects present challenges for the current generation of galaxy and galaxy cluster formation models, which
fail to reproduce this kind of source in the numbers and luminosities seen, but better
statistics on this population and a better understanding of the processes driving their
activity are needed for progress to be made.
Y.Sophia Dai
We study the relationship between AGN and star formation in a sample of far-infrared(FIR)
detected active galactic nuclei (AGNs). We calculated the star formation rate (SFR)
from the AGN-removed IR luminosity. We discuss the caveats in SFR estimates for
AGN systems, and the binning and selection effects in deriving the AGN-SFR correlation. We confirm that there is a positive correlation between the AGN luminosity
and SFR, after removing the redshift effect. We investigate the Eddington ratio and
supermassive black hole ( SMBH) mass and found no effects on the correlation. We find
a constant ratio between the SFR and the black hole accretion rate (BHAR) regardless
of redshift or SMBH mass. The flat mass accretion ratio has a value and scatter comparable to the accumulated mass ratios found between SMBH and host stellar mass in the
local universe. Our results support the evolution picture where the SMBH andthe host
galaxyare growing at a relatively constant rate, possibly from a common gas supply.
Gas Loss By Ram Pressure Stripping and Internal Feedback
from Low Mass Milky Way Dwarf Satellites
Andrew Emerick
Columbia University - American Museum of Natural History
The combination of ram pressure stripping, tidal stripping, and internal feedback from
massive stars dominates the evolution of infalling dwarf satellites of the Milky Way.
In the context of recent observational and theoretical work placing constraints on the
quenching timescales of dwarf satellites, we investigate the ability for ram pressure stripping and internal feedback to explain the quenching process in the smallest satellites of
the Milky Way using three-dimensional, high resolution, wind tunnel simulations. Using initial conditions appropriate for a dwarf galaxy like Leo T, we investigate whether
or not environmental gas stripping and internal feedback together can quench these low
mass galaxies on the expected timescales, shorter than 2 Gyr. We find that internal
feedback in these low mass galaxies is too infrequent to have a significant effect on the
stripping evolution, in contrast to feedback in more massive galaxies. Our results show
that ram pressure stripping operates less efficiently than expected on low mass dwarfs,
requiring additional physical processes to account for the whole picture of dwarf satellite quenching. I will discuss these results and briefly discuss the possible roles tidal
stripping, group pre-processing, and reionization may play in quenching these low mass
dwarf galaxies.
The geometry of the AGN obscurer in a hyperluminous quasar
Duncan Farrah
Virginia Tech
We study the geometry of the AGN obscurer and ongoing rates of star formation in
IRAS 09104+4109, an obscured hyperluminous quasar at z=0.442, using infrared data
from Spitzer & Herschel, X-ray data from Nustar, Suzaku, and Chandra, and an optical
spectrum from Palomar. The infrared data can be reproduced by a smooth AGN
torus with a viewing angle (from pole-on) of 38 degrees and a half-opening angle of
39 degrees, and a starburst with a star formation rate of 126 Solar masses per year.
Combined with previous work, this is consistent with iras having undergone at least
two epochs of luminous activity in the last 200Myr: one approximately 150Myr ago,
and one that is currently ongoing. The inferred ages of the current starburst, and the
radio jets, suggest that the two are not directly associated. The X-ray and infrared
data are both consistent with axisymmetric, coaligned, toroidal obscurers in which the
line of sight viewing angle is close to, but larger than, the half-opening angle of the
torus. This ‘skimming’ of the edge of the torus is consistent with no broad lines being
visible in direct (optical) light. The X-ray data further suggest a photon index of 1.8
and a line-of-sight column density of 5e23cm-2. This argues against a fully reflectiondominated hard X-ray spectrum. Both the X-ray and infrared data are consistent with a
bolometric luminosity of 1.3-6.5e13Lsun. Combining constraints from the X-ray, optical
and infrared data suggests that the bulk of the infrared and X-ray torii are within a
vertical height of 20pc, and a radius of 200pc, of the nucleus.
TCB Flash: Constraining the Timescale for Satellite
Quenching in Local Group-like Environments
Sean Fillingham
UC Irvine
Current hydrodynamic and semi-analytic models of galaxy formation fail to reproduce the observed fraction of passive satellite galaxies across a broad range in satellite
stellar mass. This discrepancy hinges on a general lack of understanding regarding
the physics by which star formation is suppressed, or quenched, in over-dense environments.Comparing detailed observations from the SDSS and the Local Group with
subhalo distributions in cosmological N-body simulations, we measure the timescales
upon which a typical satellite galaxy quenches after falling into the virial volume of its
host system. By constraining this timescale, we are able to infer the physical mechanisms likely acting on these systems and begin to piece together a coherent picture
of satellite quenching, spanning more than 5 orders of magnitude in stellar mass. In
particular, our results indicate a critical mass scale at which ram pressure stripping
likely becomes the dominant quenching mechanism in groups and clusters, including
our own Local Group.
Induced star formation in interacting galaxy pairs
Isaura L. Fuentes-Carrera
ESFM, Instituto Politecnico Nacional, MEXICO
”The correlation between enhanced star formation (SF) and external perturbations
is not straightforward. Models and observations show a clear SF enhancement and
SF efficiency increase as separation between merger nuclei decreases, suggesting that
the starburst phase occurs at a late stage of merging and is confined to the central
kiloparsec. However, enhanced SF is also seen in early interactions and it does not
always come from the central parts but from the outskirts. In this work, we present
a 3D kinematical analysis of early interacting galaxies. Using scanning Fabry-Perot
interferometry Halpha observations, we derived the extended kinematics of the ionized
gas in order to study the contribution of circular and non-circular motions. We searched
for any type of perturbation that may be related to enhanced SF in order to characterize
the mechanisms involved in the SF processes in this type of systems.
Tracing the role of active nuclei in galaxy transformation: HI
absorption surveys out to z = 1
Marcin Glowacki
University of Sydney
Powerful active galactic nuclei (AGN) provide a key mechanism for transforming massive galaxies from gas-rich star-forming systems to passively-evolving red galaxies. In
particular, radio jets from an AGN can couple directly to the cold interstellar medium
(ISM) of their host galaxy. There is growing evidence (e.g. Morganti et al. 2003)
that jet-driven outflows of neutral gas can rapidly deplete or even remove the cold gas
reservoir in these galaxies.
When seen in absorption against the continuum emission of radio-loud AGN, the 21-cm
line of neutral hydrogen (HI) can provide a powerful probe of these cold gas outflows,
but until very recently observational evidence was largely restricted to nearby objects
(redshifts of z < 0.15). In this talk, I will present some early results from commissioning
the new Australian SKA Pathfinder (ASKAP) radio telescope, probing HI absorption
across the largely unexplored epoch between z = 0.4 and 1. I will discuss how these
results inform us on prospects for future large-area HI surveys of the evolving radio
AGN population.
MegaMorph and how it can identify key galaxy types
Boris Haeussler
ESO Chile
The build-up of the galaxies that populate the red sequence from the star-forming
galaxies in the ‘blue cloud’ is the key to understanding how those most massive galaxies
form. Several processes have been suggested for this transformation and are the main
topic of this conference, e.g. major and minor mergers, SF quenching and in-situ starformation, which can all move and add mass to the red sequence as a whole. Each of
these processes leaves a characteristic imprint on the galaxy light and colour profiles.
In order to identify their importance, both the identification of the respective samples
and the accurate measurement of their properties is vital.
In this talk, I will introduce how GalfitM - a multi-band version of Galfit, developed by
the MegaMorph project - can be used for both these purposes by measuring light profiles
in multiple bands (or even IFU data) simultaneously and in a consistent manner. I will
show that this leads to more secure measurements of galaxy properties - and hence a
more secure identification of galaxy populations needed to examine the transformation
of galaxies. While I will demonstrate that this new method allows a cleaner separation
of bulge- and disk-components in galaxies, I will concentrate on one-component profiles
in this talk and how they can be used to identify the key observables in the processes
mentioned. Using a sample from the GAMA survey, I will show how galaxy structural
parameters, such as half-light radius and Sersic index, vary from near-UV to optical to
near-IR wavelengths. This provides an alternative way of quantifying colour gradients
and identifying the radial change of stellar populations in galaxies.
ChangHoon Hahn
New York University CCPP
The GMRT 150MHz All Sky Survey
Preshanth Jagannathan
We present the 150MHz radio sky survey by the GMRT spanning 3.6pi steradian of
sky from -53 dec to +90dec covering 90% of all visible sky. The extracted 5336 image
mosaics with a median rms noise of 3mJy and the associated high reliability seven sigma
source catalog of 0.623 million sources are available publicly. The processing of this
survey utilizing archival data was made possible due to innovative direction-dependent
ionospheric phase correction algorithms and, a fully automated parallel calibration and
imaging pipeline. At greater depth and higher resolution than NVSS, we hope the
surveys acts as an essential low frequency resource in the study of galaxies and AGN.
Spectroscopic Bulge-Disc Decomposition of SDSS-IV/MaNGA
Evelyn Johnston
ESO, Chile
One can see an IFU datacube of a galaxy as simply a stack of images at each wavelength
step. If the S/N and spatial resolution is sufficiently high, features, such as the bulge,
disc, spiral arms etc., can be distinguished in each image. In such cases, it is possible to
decompose the datacube of the galaxy wavelength-by-wavelength to spectroscopically
separate the light from each component, and thus measure their independent starformation histories. To boost the amount of information one can extract from the data,
the best approach for this decomposition would be to use all the information in the
cube simultaneously. Such an approach is now possible with GALFITM, a modified
version of Galfit that is able to fit multi-waveband images of galaxies simultaneously to
produce one wavelength-dependent model.
This new approach to galaxy fitting has been developed and tested using commissioning
data from the SDSS-IV Mapping Nearby Galaxies at APO (MaNGA) survey. We will
present an overview of this new technique and along with some preliminary results for
the bulge and disc star-formation histories of lenticular galaxies within the MaNGA
Quenching of star formation in massive galaxy clusters -Lynx
W caught-in-the-act
Inger Jorgensen
Gemini Observatory
In massive galaxy clusters the interactions between galaxies and cluster gas as the
galaxies enter the cluster for the first time may lead to quenching of the star formation.
This interaction transforms them into passively evolving bulge-dominated galaxies. We
present evidence for a cluster ‘caught-in-the-act’ at redshift 1.27. The Lynx W cluster
contains a significant population of bulge-dominated galaxies with very young stellar
populations and/or low-level star formation. The population is present throughout the
cluster. We link this population to our larger sample of bulge-dominated galaxies in rich
clusters spanning from the present to redshift 1.27. In total, our data currently cover
eight clusters at z=0.2-1.27 with deep spectroscopic data and Hubble Space Telescope
imaging. We find substantial cluster-to-cluster variation of the galaxy populations, but
also the expected signature of passive evolution of bulge-dominated galaxies from z∼1.3
to the present.
Hidden in plain sight: Mass segregation using galaxy
analogues in simulations
Gandhali Joshi
McMaster University
We use high resolution DM-only simulations to explore the mass functions and radial
distributions of subhalos in group and cluster halos with two popular halo finders: the
Amiga Halo Finder (AHF) and ROCKSTAR. There are significant differences in the
subhalo radial distributions, due in large part to differing subhalo hierarchies. Instead
of looking strictly at subhalo populations, we identify a sample of ‘galaxy analogues’
and show the radial distribution of these analogues agree well at large halo-centric
radii, but still show significant differences at small separations from the host halo centre where phase-space information becomes important for disentangling the analogues
from the dense host mass distribution. The extent to which galaxies are segregated by
mass within their parent halos is a currently unresolved topic that could shed light on
environmentally-driven mechanisms of galaxy evolution. We explore mass segregation
in our parent halo population using the identified galaxy analogues. Like some previous work, we see evidence for mild mass segregation at small radii (within 0.5Rvir)
with average galaxy analogue mass decreasing with radius. We also see evidence that
beyond a virial radius, the average galaxy analogue mass tends to increase with radius.
These mass segregation trends show a further dependence on halo mass with the trends
becoming weaker in more massive halos. Our findings suggest that the observed mass
segregation trends are likely dominated by the accretion history of the subhalos rather
than dynamical friction, particularly in massive clusters. We are currently extending
this study with SPH group and cluster simulations.
The Distribution of Active Galactic Nuclei in Massive Galaxy
Clusters at z∼1
Wenli Mo
University of Florida
We present an analysis of the distribution of active galactic nuclei (AGN) in ∼2000
galaxy clusters at z∼1 from the Massive and Distant Clusters of WISE Survey (MaDCoWS). At this epoch, MaDCoWS provides the most coverage of the extragalactic sky.
We use existing catalogs from literature of AGN selected based on their optical and
mid-infrared colors and radio emission. Stacking the radial distribution of AGN in
MaDCoWS galaxy clusters, we find a distinct overdensity in quasar excess within 2’ of
cluster center. For radio AGN, this overdensity is concentrated to within 1’ of cluster
center. We also investigate the dependence of the cluster AGN distribution on cluster
mass and central radio activity, and quantify the fraction of clusters hosting extended
radio sources at this epoch.
Physical properties of star-forming and quiescent galaxies at
Hooshang Nayyeri
UC Irvine
”In this work we investigate the far infrared properties of star-forming and passively
evolving systems at z∼3 in the five CANDELS fields as identified from LBG and
4000A/Balmer break selections. We use the Herschel/SPIRE observations in the 250,
350 and 500 microns to construct a stacked far infrared SED of the different populations.
This along with the stacked optical and near infrared observations from CANDELS reveal information on the SFR and dust temperatures of these galaxies. This together
with the mass and SFR measured for individual sources from SED fitting would help
us in better understanding the evolutionary path of each population at z∼3. ”
Probing the transformation of galaxies in clusters at
high-redshift using dynamical analyses
Lyndsay Old
University of Toronto
Galaxy clusters host the most massive galaxies in the Universe. As such, observations
of galaxy clusters deliver not only the properties of galaxies at the time we observe
them, but also give us insight into how they form and evolve over cosmic time. Dynamical analyses of high-redshift cluster galaxies provide a way of extracting both the
local and global dynamical history of todays massive galaxies. These analyses separate
galaxies that reside in dynamically distinct subgroups, which are likely to have been
recently accreted and also characterise the history of the galaxys global environment,
for example, by deducing whether clusters exhibit signs of a recent merger. To date,
dynamical analysis has been generally restricted to clusters at low-redshift due to lack of
spectroscopic redshifts for member galaxies. I will present new results on the dynamical
analyses of ten galaxy clusters at z∼1, for which there are an unprecedented number of
spectra at this epoch. In particular, I will discuss i) the fraction of infalling galaxies that
are in sub-groups, ii) how dominant massive red galaxies are in the infalling subgroup
population, iii) how properties such as star formation in these infalling subgroups differ
from virialised galaxies. I will discuss the implications that these results have on the
transformation of galaxies in dense environments and how these results compare to the
evolution of cluster galaxies from z∼1 to the current day in cosmological simulations.
Exploring the merger-starburst connection and its impact on
the observed bimodality in galaxy properties
Milena Pawlik
University of St Andrews
The observed diversity in galaxy properties as well as the varying frequency of different galaxy types throughout cosmic time point to a complex evolutionary picture
with a range of possible pathways: from evolution in isolation, through that affected
by the environment, to violent galaxy interactions and mergers. Transformations along
the pathways may lead to present-day galaxies having remarkably divergent properties
from their initial states, which makes the disentangling of the different effects challenging. The short-lived (post-)starburst (SB/PSB) galaxies, that show evidence of
an historical rapid increase and subsequent quenching in star formation, may provide
an insight into one of the processes governing galaxy evolution. Theoretical modelling
has shown that they could be a result of gas-rich major mergers, and consequently, a
transitional population linking the star-forming ‘blue-cloud galaxies and the passively
evolving spheroids populating the ‘red sequence’. The aim of this work is to explore the
merger-starburst connection and to learn about the significance of the PSB galaxies in
the formation of the observed bimodality in galaxy properties, through analysis of the
morphology and structure of galaxies at different stages of the SB/PSB phase.
I will introduce the shape asymmetry, a new automated measure designed to quantify
morphological disturbance in galaxy outskirts (Pawlik et al. 2016), that we combine
with pre-existing structural parameters to study the evolution of galaxies throughout
the (post-)starburst phase. Our analysis of an evolutionary sample of SB/PSB galaxies
(Wild et al. 2010) revealed that ∼50% of galaxies with very recent starbursts (<0.1
Gyr) show morphological features characteristic of a recent merger, and that this fraction declines with the starburst age for the next 0.5 Gyr - a trend resembling that
expected for post-mergers with fading tidal features. The lack of significant evolution
in their central concentration of light suggests that local SB/PSB galaxies do not attain
the highly concentrated structure characteristic of galaxies populating the present-day
red sequence during the first 0.6 Gyr after the starburst.
I will finish by presenting our more recent work where we investigate the dependence
of the evolutionary pathways of SB/PSB galaxies on their stellar mass and extend to
samples of older PSB galaxies (<1.5 Gyr), and I will compare the morphological and
structural properties of SB/PSB galaxies to those of post-mergers modelled in hydrodynamical simulations.
Understanding the galaxy transformations leading to dwarf
Reynier Peletier
Kapteyn Institute, University of Groningen
I will describe some recent results of the Fornax Deep Survey, a deep multicolour imaging survey using the VST at ESO, together with followup longslit and IFU spectroscopy,
about the formation of dwarf galaxies. I will discuss the effect of the cluster environment on the evolution of galaxies by comparing a new catalog of faint galaxy debris
around the central Fornax cluster galaxy NGC 1399 with debris in the field (from Duc
et al. 2015) and the Virgo cluster. I will also compare in detail dwarf ellipticals in
Fornax with dwarf irregulars in the field, by comparing properties such as abundance
ratios of various elements, surface brightness profiles in the outer regions, and kinematical support, to answer the question whether and how dwarf ellipticals originate from
dwarf irregulars, and what the role of the environment is in this process.
Reynier Peletier
Kapteyn Institute, University of Groningen
MHD simulations of ram pressure stripping of a disk galaxy
Mariana Ramos-Martinez
The removal of the ISM of disk galaxies through ram pressure stripping (RPS) has been
extensively studied in numerous simulations. These models show that this process has a
significant impact on galaxy evolution (the truncation of the ISM will lead to a decrease
in the star formation and the galaxy will become redder). Nevertheless, the role of the
magnetic fields (MFs) on the dynamics of the gas in this process has been hardly
studied, although the influence of magnetic fields on the large scale disk structure is
well established. The presence of MFs produce a less compressible gas, thus increasing
the scale height of the gas in the galaxy, that is, gas can be found farther away from
the galactic potential well, which may lead to an easier removal of gas. We test this
idea by performing a 3D MHD simulation of a disk galaxy that experiences RPS under
the wind-tunnel approximation.
Nearby velocity-offset AGN: signposts of double supermassive
black holes?
Hsin-Yi(Jenny) Shih
Gemini Observatory
Galaxy mergers should result in large numbers of double supermassive black holes
(SMBHs), and these objects may play an important role in shaping some of the galaxies
that we see today. For example, The low central stellar density of luminous ellipticals
is hard to explain unless it is the result of a small-separation black hole pair losing
angular momentum to the surrounding stars, ejecting them from the galaxys nucleus
(Begelman et al. 1980; Postman et al. 2012). However, few double SMBHs have been
detected to date. A recent search for AGN whose emission lines are offset in velocity
from the stellar nuclei of their host galaxies has turned up >300 objects that appear
to be “offset AGNs” that are in the process of joining the presumed SMBH at the
galaxy’s center (Comerford & Greene 2014). To confirm whether these objects are
genuinely offset AGNs, we observed 7 of the closest offset AGN candidates (z < 0.03)
with IFU spectroscopy and deep imaging. These data can help us either confirm the
offset/double-AGNs or, if they are not double SMBHs, identify the nature of the objects
that are confusing this seemingly promising method of finding double SMBHs through
The MOSDEF Survey: Dissecting the star-formation rate vs.
stellar mass relation at z ∼ 2
Irene Shivaei
UC Riverside
We investigate the correlation between stellar mass and star-formation rate (SFR)
among star-forming galaxies at the critical epoch around z ∼ 2, from the MOSFIRE
Deep Evolution Field (MOSDEF) survey. The MOSDEF survey is a multi-year project
that uses the near-IR MOSFIRE spectrograph on the Keck telescope to characterize
the gaseous and stellar contents of ∼ 1500 rest-frame optically selected galaxies at 1.37
< z < 3.80. The SFR-M∗ relation is commonly used to distinguish star-forming and
quiescent galaxies. Based on a representative sample of 264 galaxies with H-alpha and
H-beta spectroscopy, we have estimated robust dust-corrected instantaneous SFRs over
a large dynamic range in stellar mass (∼ 109 - 1011.5 M ) to quantify the SFR-M*
relation. We find that different assumptions for the dust correction, such as using the
color excess of the stellar continuum to correct the nebular lines, sample selection biases
against red star-forming galaxies, and not accounting for Balmer absorption, can yield
steeper slopes of the SFR-M* relation. Moreover, We compare the SFR-M* characteristics based on the SFR(H-alpha) with those of the SFR(UV) derived from the stellar
continuum at 1600 A. We argue that in the absence of direct measurements of galaxyto-galaxy variations in the attenuation curves and the initial mass function, the larger
scatter in SFR(H-alpha)-M* relation compared to that of the SFR(UV)-M* relation
can not uniquely be attributed to the stochasticity of star formation in high-redshift
galaxies. Separately, by incorporating mid- and far-IR data from Spitzer and Herschel,
we have a direct probe of dust obscured star forming regions that might be missed
by Balmer lines. We investigate panchromatic SEDs of our galaxies that are individually detected in the IR bands, using the extensive photometry from 0.3 - 500 µm, and
present the first direct comparison between Balmer line and panchromatic SED-based
SFRs for z ∼ 2 galaxies.
Star Formation in Interacting vs. Spiral Galaxies in the Local
Beverly Smith
East Tennessee State University
”We have extracted UV/optical/IR fluxes for ‘clumps’ of star formation in sample
of nearby interacting galaxies, derived their star formation rates, and compared with
regions in normal spiral galaxies. We have used archival Hubble Space Telescope images
to investigate the star cluster population in the most luminous of these clumps. The
luminous knots of star formation in nearby interacting galaxies are good local analogs
for clumps found in high redshift galaxies.”
Sizes and mass profiles of post-starburst galaxies at z∼1.5
Katherine (Wren) Suess
UC Berkeley
Observations over the last decade have revealed that quiescent galaxies were much
more compact at earlier epochs. Several mechanisms have been proposed to form these
extremely dense galaxies, including compaction via violent disk instabilities or minor
merging, gas-rich major mergers, and dissipational collapse formation. Post-starburst
galaxies are the optimal test cases for these formation mechanisms, as they are the direct, unpolluted products of the quenching process. Recently quenched post-starburst
galaxies at z > 1 have been shown to be more compact than starburst or quiescent
galaxies at similar redshifts. These studies characterized post-starburst galaxy sizes
based on the half-light radius; however, the half-mass radius could differ and is needed
to verify the finding that post-starburst galaxies are indeed more compact than their
progenitors. We use photometric data from CANDELS to perform pixel-to-pixel spectral energy distribution fitting of 20 post-starburst galaxies at 0.7 . z < 2 selected by
their dominant A-type star population. This allows us to generate mass profiles and
confirm the sizes of post-starburst galaxies. Pixel-to-pixel SED fitting also allows us
to investigate galaxy age gradients. Together, the sizes and age gradients allow us to
discriminate between the different proposed scenarios for forming compact quiescent
The Importance of Black Hole Mass in the Physics Behind
Bryan Terrazas
University of Michigan
Using the Henriques et al. (2015) semi-analytic model, Terrazas et al. (2016) found that
quiescence is primarily a function of black hole mass, where central galaxies become
quiescent when heating from their active galactic nuclei becomes sufficient to offset
the cooling rate. We present an analysis of observational data of local central galaxies
with directly-detected black hole mass measurements in order to test this correlation
and determine the main physical drivers of quiescence. We find that the specific star
formation rate is a smooth and tight function of the black hole mass-stellar mass ratio,
or what we call the black hole prominence, for all galaxies of different morphological
types. As a result, partially-quiescent galaxies - which have generally been thought
of as transitory stages towards complete quiescence - are found to be stable systems
with intermediate black hole prominence. Further, we compare our observational data
with four state-of-the-art galaxy formation models. We find that models that balance
gas cooling with AGN heating in order to grow the quiescent population show the
best agreement with observational trends that relate black hole mass, stellar mass,
and star formation rate. Our results provide strong evidence that the black hole has
an increasingly suppressing, smoothly varying effect on the star formation occurring
within central galaxies, giving credence to the AGN feedback paradigm.
Resolving distant quasar host galaxies with high angular
resolution techniques
Andrey Vayner
”University of California, San Diego
We will present the latest results from an OSIRIS-LGS survey to resolve and study highredshift (z = 1.4 - 2.5) radio-loud quasar host galaxies. Keck Adaptive Optics (AO) with
OSIRIS provides the necessary resolution and contrast to remove the bright-unresolved
quasar emission to study the underlying faint host galaxy with unprecedented sensitivity. Thus far, our radio-loud sample consists of eight high-redshift quasar hosts with
ionized gas emission resolved at sub-kiloparsec scales, yielding essential constraints on
the galaxies dynamics, morphologies, star formation rates, metallicities, and nebular
emission diagnostics. We combine OSIRIS and AO observations with multi-wavelength
data sets from Atacama Large Millimeter/submillimeter Array, Hubble Space Telescope, and Very Large Array to better understand the multiple phases of the ISM and
stellar population properties of the hosts. These quasar hosts show evidence for both
concurrent star formation and extended quasar narrow line emission over 1 to 20 kpc.
Powerful outflows are observed along the path of the radio jets and lobes, with a suppression of star formation by a factor of 10 in some sources compared to other regions
of the host galaxies.
Compact Groups in the Millennium Simulation
Trey Wenger
University of Virginia
The importance of compact groups in galaxy formation, both at the present time and
throughout the history of the Universe, remains an open and interesting question. To
investigate this question, we developed an algorithm to identify and characterize compact groups in the Millennium Simulation. Using various clustering tools and selection
criteria, we select compact groups of galaxies from each redshift snapshot of the simulation between z∼11 and z=0. We find that the fraction of non-dwarf galaxies in
compact groups peaks at ∼1% near z∼1-2. By tracking individual compact group
members through the simulation, we find that compact groups rarely, if ever, dissociate. At z=0, about 5% of galaxies have been members of compact groups at some point
in their history. We plan to extend this analysis to include dwarf galaxies using the
much finer resolution of the Millennium-II Simulation.
The prevalence of dwarf galaxy compact groups over cosmic
Christopher Wiens
University of Virginia
”Galaxy interactions are critical to the evolution of the universe, influencing everything
from star formation to the structure of the known universe. By studying at galaxy
interactions through computer simulations, we are able to observe what would normally
take billions of years to progress. ‘Compact groups’ are extremely dense assemblies of
at least 3 galaxies and typically no more than 10 that are interacting gravitationally.
These groups yield much information about galaxy interactions and mergers in dense
environments but are difficult to observe at high redshifts. Compact groups of only
dwarf galaxies probe a regime of galaxy evolution that has been hypothesized to be
common in the early universe. Here we investigate the populations of such dwarf galaxy
compact groups in numerical simulations. In particular, the Millennium II Simulation
is a massive n-body simulation of cold dark matter particles on a time scale equivalent
to the known universe. This simulation allows us to study high redshift objects and
timescales of billions of years. Our preliminary findings indicate that these dwarf galaxy
compact groups do exist in both the Millennium and Millennium II simulations. In both
simulations, there is a large number of dwarf compact groups with an evolution track
that mirrors more massive compact groups with a peak in groups around a redshift of
Author Index
Louis, 3
James, 23
Katey, 45
Stacey, 21
Omar, 40
Philip, 29
Felipe, 45
Josh, 3
Y.Sophia, 47
Behnam, 26
Timothy, 7
Andrew, 48
Andreas, 38
Duncan, 17, 48
Robert, 38
Sean, 49
Decker, 2
Isaura, 49
Rachael, 13
Angela, 46
Gurtina, 25
H.Jacob, 10
Sarah, 28
Marcin, 50
Pierluigi, 46
David, 47
Alison, 43
Alison, 7
Boris, 50
ChangHoon, 51
Fred, 15
Shoubaneh, 2
Phil, 15
Chao-Ling, 29
Wenli, 53
Jorge, 9
Francisco, 22
Preshanth, 51
Evelyn, 51
Inger, 52
Gandhali, 52
Hooshang, 53
Allison, 26
Kristina, 20
Lyndsay, 54
Matt, 34
Jeyhan, 31
Dale, 19
David, 1
Mariska, 37
Milena, 54
Reynier, 55, 56
Pablo, 41
Bianca, 1
Gergely, 39
George, 11
Lauranne, 16
Kirsten, 12
Federico, 27
Ute, 28
Mariana, 56
Jeffrey, 4
Jessica, 34
Kate, 37
Wiphu, 43
Allison, 33
Crystal, 4
Elizabeth, 39
Anne, 19
Simona, 21
Anna, 40
Marja, 6
Hsin-Yi(Jenny), 56
Irene, 57
Brooke, 17
Rebecca, 5
Beverly, 57
Greg, 5
Martin, 12
Andra, 32
Katherine, 58
Jeremy, 25
Ezequiel, 11
Vivian, 16
Junko, 10
Tanya, 20
Andrey, 59
Trey, 59
Andrew, 33
Christopher, 60
David, 44
Gillian, 32
Bryan, 58